Smith was born in Kirkcaldy where he also attended school. He began attending Glasgow University at age 14 and subsequently moved to Oxford for a bit and lived in Edinburgh before returning to Glasgow as a professor age 28. Therefore I think it's unlikely he spoke with a Glasgow accent. It's likely he intended to write in the standard English of the day given his position in the top echelon of British academia. Glaswegian Scottish isn't really a thing, at least in that context.

I grew up a few miles from Kirkcaldy, mother taught economics at the college there, so Smith was a strong presence in my childhood.