George has no frame of reference at all here. He must have been working so hard at the office as he has obviously never heard of this programme or read any tabloids. When he asks 'who?' he may actually be asking who Jill is; another friend of Lynne's. In fact he is asking who this celebrity is. If you ask me, if a friend of my wife's was dating a celebrity, it'd be big news in the neighbourhood.
So George, having not known that Jill had been to dinner with a celebrity, instead of asking who the celebrity was, or just being amazed that Jill had been out with a celebrity, asks if he was a fussy eater, as if that could be the only reason a dinner didn't go well. It's the sort of thing your grandfather would say.
Finally, there is no way this celebrity was only into insects for his food. I've seen that programme, and I'm guessing George and Lynne haven't as they're from the 70s, and the celebrities who come out never want to eat those insects again. So I'm gussing Lynne is making a joke. George, not knowing it was a joke, is now so completely disgusted that he can't finish his dinner. It must be very easy to put George of his food if all you have to do is just mention eating insects. He is about to stand up, presumably to run to the toilet. So well done Lynne, you have ruined dinner. In fact I blame George for not knowing about this beforehand; he could have seen it coming and changed the conversation.
Who was the celebrity? Probably Joe Swash.