First let me say that I don't believe it is a real spell.
The thing we need to realize is that Ron did not know enough spells to differentiate between fake and real spells. Mr and Mrs Weasley would have used Nonverbal Spells at home.
We also know that Ron blindly trusted his brothers which is normal at that age.
“So we’ve just got to try on the hat!” Ron whispered to Harry. “I’ll kill Fred, he was going on about wrestling a troll.”
Harry Potter and the Sorcerer's Stone, Chapter 7, The Sorting Hat
“I’d worked that much out for myself, funnily enough. What happens if you break it, then?”
“You die,” said Ron simply. “Fred and George tried to get me to make one when I was about five. I nearly did too, I was holding hands with Fred and everything when Dad found us. He went mental,” said Ron, with a reminiscent gleam in his eyes. “Only time I’ve ever seen Dad as angry as Mum, Fred reckons his left buttock has never been the same since.”
Harry Potter and the Half-Blood Prince, Chapter 16, A Very Frosty Christmas
Most probably Ron was nervous after all he had five brothers who have been to Hogwarts, he would have definitely been nervous. Knowing Fred and George those guys would have thought it was fun to scare Ron.
Generally younger siblings trust their elder siblings. My brother had me believing in lots of silly stuff when I was a kid!