Hmmm. I didn't watch the whole thing. He sounds like he doesn't understand how Duolingo worked in the first place. He gives the impression that he thinks people using the app were talking to actual teachers when they used it! Whatever the pros and cons of AI in general, there's a big difference between teachers using AI to create resources and ditching teachers altogether by plonking kids in front of a computer. That's not going to happen anyway, because working parents need supervision for their kids.
Incidentally, I'm a languages teacher, have used Duolingo myself and have loads of students who do extra practice on it or learn another language on top of the ones they do in school. I think it's great!