It's really quite odd that a vegetarian would NOT check before tasting. Specially in the case of pizza, for gosh sakes! I mean, it's downright strange. People who are worried about whether things might contain meat always ask, in my experience.

Why on earth would anyone automatically assume that a free sample of pizza was vegetarian if they had not already been told it was vegetarian?

Seems to me that we might be missing part of the story.

Vegetarians are used to the fact that the majority of prepared food around them in western society is not so likely to be vegetarian, and they do ask.

Maybe the entire thing was a setup so that Gordon Ramsay could get some controversial publicity and a few laughs on his show... ;-) Consider that possibility.