The "Sound Guy" is good! 1. He has to filter Deen's Vocals out of the noise that the drumkit produces. 2. The guy recording the gig is standing almost in the first row. That means the sound he records is mostly the raw stage sound and not the mix of the PA system.
It's not easy to mix a singing drummer. His mic will always catch the drums noise (and the headset mic like the one Deen is using are very sensible to noise and feedback). Plus, the guy filming is very near the stage and far from the PA system, so the camera recorded the raw sounds of the instruments and not the final mix
