Probably had nothing to do all season but lift weights so I'd assume he would get bigger. Plus guys in their first year out of school are always skinny so it's probably natural. Iggy was on his twitter raving about how good of a shooter Jason was when they were working out together. He'll never have a post game his jumper and athleticism will keep him a job and he's more useful than Sam.
Just watched the vid again damn Jason got some arms on him