What the heck? Is that supposed to be a lot? I feel like I do that quite easily whenever i go shoot around for 60-90 minutes. That's by myself, outside where the ball can bounce anywhere, and I'm not exactly in NBA shape. Put me inside with more than one ball and I feel like I could double my number of shots. If I actually had someone rebounding for me or feeding me the balls, God only knows.
Not to mention, if I personally was an NBA player, or even a regular joe who didn't have to work, I'd easily be shooting for a minimum of 3 hours a day total. I'd probably approach it like a 40 hour a week job (at least 5.7 hours a day spent on my game, including games/practices/weights/conditioning, not including commute).
If you took a shot every 10 seconds you could shoot 500 in ~83 minutes. 83 minutes of fun, and the reward is hundreds of millions of dollars, fame, women, power, legacy, etc.
Granted I know he's not in the NBA, YET, but you have to imagine most of the NBA's good shooters took way more shots than that on average growing up. Go to the gym for 2 hours at a time 3-5 times a day, and you'd be surprised how many shots you could shoot.