How are calisthenics guys in nyc so muscular?

At first i thought it was just the low body fat but they have large muscles as well from what seems like doing well over 15 reps on a lot of there sets. Imo it looks like they tire themselves out with condition then when they’re tired they go back into normal 8-15 rep ranges which is where they start to build muscle.

These guys don’t do a lot of advanced skills like handstand push ups or anything. What gives?