A helicopter, be it a model or a full size one, is an inherently unstable and dangerous craft by it's very design. One hundred per cent concentration at all times is needed to fly one, it only takes a millisecond's loss of concentration and you are in big trouble. I know, I've done it... I managed to fly my Chinook backwards into my 'man area' and believe me, that hurt, even though I was wearing jeans. A set of rotor blades striking bare skin is going to hurt more, and if they strike the head...well, we know what can happen.
My Chinook was electric powered...the heli that struck this poor guy was a 700 sized one, I believe. Those rotor blades would have been travelling at a far greater speed than my Chinook's were, and capable of doing immense damage to bare human flesh and blood.
I guess that this young pilot, expert or not, could have had that momentary loss of concentration...it's easy enough. Something catches your sight out of the corner of your eye, an insect buzzing around your head, a sudden noise somewhere, and you have that recipe for disaster.
Then there's mechanical failure, or radio problems to consider, maybe a less than fully charged battery, contaminated fuel...the list is endless.
I guess we all know that model flying is hugely satisfying, but it can be dangerous at the same time, as this unfortunate pilot found out...may he rest in peace. But if the media really get their teeth into it, I doubt he will.