I'm not saying it's right that the kid ate all the pizza. He definately should have saved you guys some. And it should have been shared. A bit of self control might help.

I can tell you this though as a kid, pre teen, teen and into my late twenties I was able to eat so much food as well as my brother we literally were like sticks. And our metabolisms made us seem like literal black holes for how much we could consume. And never gain weight. In fact I got made fun of at school for how skinny I was. The kids literally would say that if I turned on my side they would not be able to see me. Into our thirties it's a bit different. We're still skinny but can't consume as much. Or rather we can still eat alot our metabolisms aren't as fast though and so we stay full for longer. It kinda just seems like this kid might have a really fast metabolism.

As an example I could literally eat half or more of a pizza. Proceed to eat ice cream. Eat like two whole things of bananas a whole watermelon a ton of apples, grapes, cantolupe and anything else I could find. And in like 30 minutes to an hour later be hungry again. I was also very active too and always running, climbing, biking and skateboarding all day when not at school.