The only way to really tell is to put a stop watch on him. So, I did so several times for this video and I come up with about 3.8 sec +., which is indeed fast . . .particularly for a RHB. This would be well above average for a HS player or for any RHB at any level for that matter. Putting a stopwatch on him during a live game with be the best way to get the best measurement.
PS: If you don't have s top watch but do have a smart phone, you can download a stop watch app and take your own measurements.