Adam Smith didn't understand that people would trade even if one of the peers was better at every single thing. He got lots of stuff right, and even some things that took until the 19th century to make into mainstream economics. But not this one.
Is it possible that he never posited the question? I'd say it unfolds naturally from his readings that it is the case. That said, isolating and framing the question and its consequences is not insignificant.
He is clearly on the opinion that specialization means the best entity (person, company, country, he talks about all three) capable of creating each product will tend to work on it, and then trade.
The theory of comparative advantages is a very unintuitive idea. There's a reason that it took until the 20th century for economists to notice it.
Adam Smith didn't understand that people would trade even if one of the peers was better at every single thing. He got lots of stuff right, and even some things that took until the 19th century to make into mainstream economics. But not this one.