Is Tobho Mott really Qohorik?

Question

Tobho Mott's name speaks for itself, it simply isn't Westerosi.

From the man's own accounts, he spent his youth in Qohor.

Ned sipped his wine and let the man go on. The Knight of Flowers bought all his armor here, Tobho boasted, and many high lords, the ones who knew fine steel, and even Lord Renly, the king's own brother. Perhaps the Hand had seen Lord Renly's new armor, the green plate with the golden antlers? No other armorer in the city could get that deep a green; he knew the secret of putting color in the steel itself, paint and enamel were the crutches of a journeyman. Or mayhaps the Hand wanted a blade? Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.
_{AGOT - Eddard VI}

Now this only mentions that he used to work in Qohor as a boy. It doesn't really establish that he was born and raised Qohorik. Not to mention, Tobho speaks clean Common Tongue as if it was his first language, without any accent or any funny manner of speech, as we see with other foreigner characters in the series. That would make sense if he were let's say a second generation immigrant, born in Westeros who went back to Qohor to learn the arts of metalwork.

But the ASOIAF Wiki is fairly certain that the man is Qohorik. Quoting them:

Tobho Mott is a Qohorik master armorer whose shop is at the top of the Street of Steel in King's Landing.

Is there any conclusive evidence in the series or George's interviews which establishes his ethnicity?

Answer 1

We can't be 100% sure where he is from but it seems incredibly likely that he is Qohorik. We know that Qohor is the only place to claim to know how to work Valyrian Steel.

The properties of Valyrian steel are well-known, and are the result of both folding iron many times to balance and remove impurities, and the use of spells—or at least arts we do not know—to give unnatural strength to the resulting steel. Those arts are now lost, though the smiths of Qohor claim to still know magics for reworking Valyrian steel without losing its strength or unsurpassed ability to hold an edge.
_{The World of Ice and Fire, Ancient History: Valyria’s Children}

We also know it was Tobho that reworked Ice into Widow's Wail and Oathkeeper and from your quote we know that he learnt that in Qohor.

"You have done good work, Master Mott," Lord Tywin told the armorer. "My steward will see to your payment. And remember, rubies for the scabbards."
_{A Storm of Swords, Tyrion IV}

And we know he is very good at putting colour into metal, he even got some red into Valyrian steel.

"Nor I, my lord," said the armorer. "I confess, these colors were not what I intended, and I do not know that I could duplicate them. Your lord father had asked for the crimson of your House, and it was that color I set out to infuse into the metal. But Valyrian steel is stubborn. These old swords remember, it is said, and they do not change easily. I worked half a hundred spells and brightened the red time and time again, but always the color would darken, as if the blade was drinking the sun from it. And some folds would not take the red at all, as you can see. If my lords of Lannister are displeased, I will of course try again, as many times as you should require, but—"
_{A Storm of Swords, Tyrion IV}

The Knight of Flowers bought all his armor here, Tobho boasted, and many high lords, the ones who knew fine steel, and even Lord Renly, the king's own brother. Perhaps the Hand had seen Lord Renly's new armor, the green plate with the golden antlers? No other armorer in the city could get that deep a green; he knew the secret of putting color in the steel itself, paint and enamel were the crutches of a journeyman.
_{A Game of Thrones, Eddard VI}

We also know that the smiths in Qohor know how to put colour into steel so the evidence suggests he definitely trained in Qohor. Seeing as he was a boy when he trained it seems likely he is at least from the Free Cities or at least Essos.

Qohorik swords, knives, and armor are superior to even the best castle-forged steel of Westeros, and the city's smiths have perfected the art of infusing deep color into the metals of their work, producing armor and weaponry of lasting beauty.
_{The World of Ice and Fire, The Free Cities: Qohor}

Lastly, we hear that those secrets of Qohor are tightly guarded so it seems very unlikely that they'd give them to an outsider, especially a boy. With all this together I'd say it's 99.99% certain he is Qohorik though with no explicit quote I can't say for sure.

Only here, in all the world, has the art of reworking Valyrian steel been preserved, its secrets jealously guarded.
...
Maester Pol's treatise on Qohorik metalworking, written during several years of residence in the Free City, reveals just how jealously the secrets are guarded: He was thrice publicly whipped and cast out from the city for making too many inquiries. The final time, his hand was also removed following the allegation that he stole a Valyrian steel blade. According to Pol, the true reason for his final exile was his discovery of blood sacrifices—including the killing of slaves as young as infants—which the Qohorik smiths used in their efforts to produce a steel to equal that of the Freehold.
_{The World of Ice and Fire, The Free Cities: Qohor}