UserID and AccountID could just as well be integers.

What he means is that by introducing a layer of indirection via a new type you hide the physical reality of the implementation (int vs. string).

The physical type matters if you want to log it, save to a file etc.

So now for every such type you add a burden of having to undo that indirection.

At which point "is it worth it?" is a valid question.

You made some (but not all) mistakes impossible but you've also introduced that indirection that hides things and needs to be undone by the programmer.