The in-universe answer to that is that of course Albus Dumbledore was not wrong here, because Albus Dumbledore is never wrong.
From an interview:
Oh yes, very much so. Dumbledore often speaks for me.
Bellatrix also provided a quote where Rowling confirms that the general statement above is also true in this specific case.
However his brother knows him best, and he says about Albus:
"I knew my brother, Potter. He learned secrecy at our mother’s knee. Secrets and lies, that’s how we grew up, and Albus. . . he was a natural." (DH)
Albus Dumbledore himself told Harry in the hospital at the end of the first year
"The truth." Dumbledore sighed. "It is a beautiful and terrible thing, and should therefore be treated with great caution."
It is possible to lie by omission, causing those listening to reach wrong conclusions, without telling anything that is technically a lie. That is why witnesses swear to tell the whole truth. As his brother points out, for Albus lying by omission is natural.
For example, Snape thinks that he is protecting Lily's son (Harry), until Dumbledore finally reveals his plans.
"You have kept him alive so that he can die at the right moment?... You have used me... I have spied for you and lied for you, put myself in mortal danger for you. Everything was supposed to keep Lily Potter's son safe. Now you tell me you have been raising him like a pig for slaughter" (DH)
And Dumbledore doesn't deny it, because it is the truth and he avoids lying. So instead in his typical style he tries to distract from the truth.
"Don’t be shocked, Severus. How many men and women have you watched die?"
"But this is touching, Severus," said Dumbledore seriously. "Have you grown to care for the boy, after all?"
So we have to ask ourselves, what are Dumbledore's motives at the moment, what does he want to achieve? Dumbledore knows that the prophecy is not binding.
"You are setting too much store by the prophecy!" ... "Would it have meant anything? Of course not! Do you think that every prophecy in the Hall of Prophecy has been fulfilled?" (HBP)
"But Harry, never forget that what the prophecy says is only significant because Voldemort made it so. I told you this at the end of last year. Voldemort singled you out as the person who would be most dangerous to him – and in doing so, he made you the person who would be most dangerous to him!" (HBP)
Even knowing this, Dumbledore does exactly the same, he is setting too much store by the prophecy, but what the prophecy says is only significant because Dumbledore believes it is.
At this point Dumbledore tries to convince Harry to follow the path Dumbledore selected for him. And somewhat untypical for Dumbledore, he tries to motivate Harry not with love but with revenge.
"Imagine, please, just for a moment, that you had never heard that prophecy! How would you feel about Voldemort now? Think!"
Harry watched Dumbledore striding up and down in front of him, and thought. He thought of his mother, his father, and Sirius. He thought of Cedric Diggory. He thought of all the terrible deeds he knew Lord Voldemort had done. A flame seemed to leap inside his chest, searing his throat.
"I’d want him finished," said Harry quietly. "And I’d want to do it."
"Of course you would!" cried Dumbledore.
Just yesterday I asked Did Voldemort mark Harry as his equal?. If you read the answers there, you can see that several people are convinced that Voldemort did mark Harry as his equal. And that means the Dumbledore also can convince himself that what he says is (a useful part of) the truth, from a certain point of view (to quote Obi-Wan Kenobi).
So from Dumbledore's point of view, saying this is not wrong, as it furthers his goals and it is not technically a lie.
Aberforth's comments refer exactly to this topic:
"I can’t. It’s got to be me, Dumbledore explained it all –"
"Oh, did he, now? And did he tell you everything, was he honest with you?"
Harry wanted with all his heart to say "yes", but somehow the simple word would not rise to his lips. Aberforth seemed to know what he was thinking.
Note that "honest" here means whether Albus told the whole truth, not whether the parts he told were a lie.
Even Harry, who really wants to believe that Dumbledore told him the whole truth, can't honestly say so.
Personally I agree with you that it doesn't make sense for someone like Voldemort to choose just one and ignore the other. It's not like there is a limit on the number of people he can kill. If there is just a slight chance that someone may eventually grow into a danger, it is a natural decision to remove the danger, like it is a natural decision for him to kill Amelia Bones because she might be an obstacle to his plans.
But to consider someone (or something) a danger doesn't mean to consider them "his equal".
You can say that he chose to attack Harry because he had the opportunity to attack Harry, but that doesn't mean he chose him as "his equal". The Potters made the mistake to choose Peter as their secret keeper, this allowed Voldemort to attack them. The Longbottoms didn't choose a Death Eater as their secret keeper. It doesn't matter from Voldemort's point of view. He has waited for almost two years since he heard the prophecy till he had the opportunity to kill Harry. Within the next years an opportunity to kill Neville would arise, before he could become a danger.
Dumbledore here claims that for Voldemort, a pureblood is the only kind of wizard worth being. Voldemort has an inflated ego, he certainly doesn't consider himself worthless. He might pretend for his followers, but the word "creed" implies that he himself believes it.
So it seems that Dumbledore is stretching the truth quite thin in his attempt to guide Harry to his ultimate suicide.