I work at a hobby shop. It was a Align T-Rex 700. Rotor span is around 3ft., per blade. Add the width of the rotor head,and you're talking almost a 7ft. blade arc.
It is believed he was performing a trick where the heli comes right at him, then reverses before it would hit him in the head. He was an experienced flyer, not a newb. All happened in front of his dad.
Third fatality this year;all experienced r.c. pilots.