Looking at his other videos this seems like a clear cut case of copyright infringement, if he's not obtaining mechanical licenses. I don't understand why anyone is up in arms about this.
But you're right that the guy is probably in the wrong. Part of the issue too is how opaque YouTube is about this kind of thing. It would be cool to see them build better appeals systems or at least treat their creators a little better than they treat copyright trolls (which may or may not be who gave him the strikes in the first place.)
Because copyright is controversial.