He was flying a Trex 700-class stunt helicopter, with a large 1.6m diameter single rotor. He was using it for complex aerobatics - high accelerations, very high turn rates, very little respect for the gravity vector.
You can't do these sorts of things at all with human-sized helicopters - they're not maneuverable enough. In fact, the increase in maneuverability as high-powered single-rotor helicopters scale down is actually a problem for human reaction time. Model helicopters conventionally used a mechanical flybar in order to make the helicopter less responsive to inputs and more controllable. More recent innovations in flybarless electronics have enabled fly-by-wire control to substantially speed up responsiveness while still permitting stable flight when desired.
A single-rotor stunt helicopter is very different from a camera multirotor. A 1.6m carbon fiber blade vs a (usually plastic) 0.1-0.4m blade. A high-powered two-stroke engine vs a battery and motors.
And very importantly, the purpose of the two aircraft is entirely different. This type of helicopter uses collective and cyclic pitch oscillations, and a rudder. That's a completely different control scheme than a normal multirotor, which uses differential thrust. It lends itself to storing energy in the angular momentum of the blades at low collective pitches (running the rotor progressively faster while hovering), and then releasing it all in a maneuver by setting the pitch higher. That means the flat, strong carbon fiber rotor blades can be travelling at a tip speed of 400mph or higher. Even a very large camera-toting quadrotor is likely to have a (plastic, thin, bendy) rotor tip speed in the 100-150mph range - they're optimized for hovering battery life, and differential throttle has limited maneuverability, and the slower & larger the better. Being so much ligher per (disposable, easy to break) prop means that even at similar tip speeds the angular momentum is much diminished.
"Video footage has emerged of Mr Pirozek, who was a world-recognised aerobatic flyer, putting his Trex 700 helicopter through a series of remarkable tricks, including one that involves dropping the $1,500 model out of the sky by turning off the engines and restarting them just before the model chopper hits his head."
https://www.youtube.com/watch?v=J0wvXoZ9KYg
Lastly, "beheaded" seems to be a linkbait overstatement, and is considered dubiously by the medically inclined - even with all the power behind those blades, the skull is a very strong thing. The eyewitness comment was that there were wounds to his scalp, which tabloids turned into "cut off the top of his head" and then into "cut off his head". There were wounds to his scalp, but the ones to his throat are likely the ones that killed him. You don't need to sever the spinal column to slit a throat with a sharp blade.