Eating pizza gain weight?

Question

10 days ago I started to work out like 20-25 minutes lifting weights then i go biking for like 1 and a half- 2hours and 2 days ago i ate a whole medium pizza from dominos i was soooo hungry and when i went to the pool yesterday i shared half a pizza with a friend. before i ate the medium pizza i weighed my self like 15 days ago and i weighed 141 pounds now i weigh 150 pounds do you think it was from eating pizza? or from gaining muscle from working out (cause muscle weighs more than fat) by the way im 13 and still growing and i might be going through my growth spurt still

Answer 1

I really don't think so,  an average slice of Pizza has less than 300 calories.

Answer 2

The only people who could put on nine pounds of muscle in two weeks are dedicated body builders who spend hours a day lifting weights. It is almost certainly either from a growth spurt or from the pizza.