Sometimes, Mengele would make the prisoners do an extra hour in the spa

Billy Joel realises that comparing a brief spell in a luxury clinic getting treated for drinking too much with being shipped off to a Nazi death camp might be a bit much:

"I hated it. It was like a concentration camp - well, I can't say that, I've never been in a concentration camp. But for me, it was.

Briefly, he realised it was a facile and offensive comparison. But then decided to go with it anyway.

"There's a lot of dogma that goes with it, and there's the whole AA thing, and for a lot of people that works. I didn't necessarily follow that."

Yes, that does sound a lot like being separated from your family, starved, getting experimented upon, being shuffled into a room and getting slowly gassed to death. Presumably someone removed Joel's sense of perspective with a pair of pliers.