Eh, I don't know. I think it's pretty common for 4-year-olds to wear clothes their parents picked out. I know I wasn't picking out all my clothing at that age. As long as the parents aren't trying to push a style that the kid dislikes, and are willing to give the child an opportunity to make choices, I don't think it's terrible if they pick out a shirt for the kid to wear and the kid chooses to wear it.
I think it's pretty lame for a kid to be wearing a shirt of a band they've never heard of, if the kids parents don't even like their music.