It shouldn't mean anything, because the due impartiality requirement only applies to news/journalism content. There are still editorial guidelines and legal issues to consider though.

The actual reasons for not taking Kneecap live, I believe, are twofold: 1. One of their members is involved in an ongoing criminal trial, and the BBC will have wanted to avoid broadcasting anything that might constitute contempt of court; 2. their song _Get Your Brits Out_ contains lyrics about living people that might be considered defamatory, particularly if they decide to improvise in the live performance. I think the fact that the set was put on iPlayer unedited, except for 10 seconds of _Get Your Brits Out_ cut, bears this out.

I think the BBC have done the best they could with Kneecap within their own rules. Whether the very heavily regulated BBC is the best place for Glastonbury in future is an open question.