I think the beef just really turned him off. Up to that point, he was really enjoying it and would finish the lamb I'd put down for him.
I'm not going to force him. I'll give him the wellness, because at least I know that's good for them all. And later I can always try it again. Maybe he just needs to forget he didn't like the beef then he will give it another try.
There are only two rules at my house: House rule #1. Cats rule. House rule #2. See rule #1.