In which case you are greatly mistaken, almost everyone has at least one guilty pleasure, one terribly simple mainstream band that they know are absolutely shit and talentless yet they for some reason enjoy listening to.
If he was saying how amazingly talented Avril Lavigne is then you might have a case, but simply saying that he enjoys some of her songs, well so what. Good for him that he can admit he gets enjoyment from simpler music, while also seemingly getting into more technical stuff. He may not have music tastes i necessarily agree with, but im sure he leads a different life, and is a different person, and looks for different things from music... no problem!
Music can be many many many things... from a great technical story, to an exploration of a mood or theme, to something to dance to, to something simple to be a backdrop for a message, etc..
All are valid, all have their uses. Its when people start claiming their music is something that it isnt, thats when theres a problem.