I feel like a black hole would be more likely to suddenly open in the middle of the Earth than anyone ever lying in these Japanese or Korean series, in any situation where it would actually matter in the greater story.
It feels weird to write this right after saying nobody ever lies, but since this is a case where it doesn't really matter, I'd say Jinwoo used a white lie to make it easier for the other S rank hunters to accept seeing their colleague/friend turned into an undead creature. Since Jinwoo actually released the healer afterwards, I'd say they are much happier this way because they didn't lose Cha, thanks to that. Cha herself must be the happiest one of them all.