Umm, he was SELLING. Nothing about his release was donation-relevant.
Actually it is relevant. He admitted right in his first message than anyone could go online and pirate the song, which is true. Buying the song effectively is a donation. (You could argue that pirating is illegal, but since Louis C. K. isn't going to come after you for downloading the performance, it's completely consequence-free.)
You can feasibly shoplift as well (not my thing, but I've looked and honestly it doesn't look difficult at many stores), but I don't think anyone is arguing that that you're 'donating' when you pay a store for your socks.
Granted, copying isn't technically theft yada yada, but it sure as hell isn't a donation when you pay the content provider a set price for the content.