I would guess he's been watching the LLWS Sultan, as he said in the first place.
To respond without any sarcasm biggerpapi, curveballs are an interesting discussion with respect to younger players. Studies have shown that throwing a curveball the right way will not hurt your arm. However, fatigue causes arm angles and arm slots to change, with further enhance injury possibilities. Young players generally have trouble repeating mechanics once that fatigue is reached, and thus potentially the reason for injuries.
It is pretty incredible to me how many curveballs are thrown in the games as well though. It'd be interesting to get some sort of biomechanical analysis on these young pitchers and to see the effects on the arm on top of all of these studies being conducted.