Thinking about it, I can't see anything in pizza ingredients that individually, a chicken shouldn't eat, and it only has a lot of salt if the meat on it is heavily salty like pepperoni, but I'm also not sure if cheese is ok, I'd have to consult the oracle of google on that, (no, I've never fed my chickens leftover pizza...( Leftover pizza? Is there such a thing?))
But I'm not sure you should do that on any regular basis, being that we are what our food eats...
Anyway, guys, don't be too hard on him, we all make mistakes, his tiny veloseraptors might get a tummy ache, but they won't die or anything, and we live and learn.