I don't think there is any conflict here, people aren't criticizing how the free market works, they're criticizing Spotify for what they see as caving. The "free market" allows companies to do whatever they want with their IP, and it also allows people who are unhappy with that company's actions to criticize them. There's nothing that's not "free market" about that.

If you are trying to make the distinction that "censorship" is a term with a specific definition that applies to government censorship, I don't think people really disagree with that either, they're just using the phrase loosely because nobody's provided a better concept to apply. Call it corpo-sensorship, or corpoship, or whatever, but until there's a better word people will just keep using the more digestible one in a lazy way.