Sure it wasn't. Jack's got enough experience to know that assimilation is never good. Daleks and Cybermen, they were all about assimilating, becoming one of the mass. The Master, with his Toclofane. The last of humanity, converted into cyborgs and forced to act together and do his bidding. Aliens that use that sort of tactic are probably close to number one on the list of things that actually do terrify Jack. Which is why, at the first sign of trouble, he'd tried to get as many people as he could out. That he hadn't managed with Eridan, that he doesn't know what it was that did happen with him, it rubs him the complete wrong way.

"Wasn't it?" he asks, directly.