If they are producing code, there is some knowledge being absorbed. Nobody is using AI to create an app is learning zero.

I think the knowledge being absorbed is 'how to use AI to make apps', not necessarily anything about the code itself. I've seen lots of people who are very effective with AI suddenly poleaxed in interviews without it. Going from 'able to explain exactly what needs to happen' to 'staring at a blank page with no ideas'.