I know this is probably a stupid question, I just wanted to get some insight.

So today some bro selling a wheel tried to convince me that a mechanic can 'rethread' or fix the threads on hubs that are stripped or damaged. Obviously I didnt buy the wheel haha, and it all sounds like a loud of BS. Is there any truth in what he was saying?

Using a threadfile. Takes a while though I heard. Why dont you call a shop?

no
he is not the smartest tool in the box

It is possible to re-thread a hub but far from practical as it would be a time consuming process that would require tools and technology your average mechanic will not possess.

And the cost would far exceed the cost of a new hub.

and be unsafe unless additional material was bonded with the stripped area