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.

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?

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?