Rolling the waistband on your shorts is something that's pretty common place all over the country in college basketball....its sort of a fashion statement
It started with HS/AAU teams sponsored by Under Armour because the UA logo is prominent on the inside waistband. Then Nike and adidas kids did it because it was popular but those brands don't logo the inside waistband.
It's starting to lose some popularity now though. Kind of like a lot of kids used to wear shooter sleeves but don't wear them as much anymore