The point is that you might pass a semantically invalid user ID. Not that you might pass an invalid UUID.
I generally agree that it's easy to over-do, but can be great if you have a terse, dense, clear language/framework/docs, so you can instantly learn about UserID.
More specifically, if all entities have a GUID, it's not impossible to accidentally map entity A ID to entity B ID accidentally, especially when working with relationships. Moving the issue to the compiler is nicer than the query returning 0 results and the developer staring endlessly for the subtle issue.
I generally agree that it's easy to over-do, but can be great if you have a terse, dense, clear language/framework/docs, so you can instantly learn about UserID.