"Angry White Boy" is a derogatory term for late 90s/early 00s nü metal generally referring to how the only people who liked it were privileged white kids who didn't really have anything to be genuinely mad about. The title isn't so much a reference to the musicians as much as the fad, which, sadly included some acts that didn't quite fit the description.
It's worth pointing out that Al did this polka around the same time that he worked with Ben Folds on "Rockin' The Suburbs". Indeed, his own Ben Folds-assisted style parody is three songs later in the album.
Paul McCartney disapproved of Weird Al's "Live and Let Die" spoof "Chicken Pot Pie" because... Paul is a vegetarian? What sense does that make? Weird Al is a vegetarian too!
For one, Al wasn't yet a vegetarian when he first wrote the song. Also, Paul (well-known for his social crusades) is one of those vegetarians. In fact, I'm pretty sure he went full-on vegan after Linda died.