Clearly, this 206 was out of control from the moment the skids left the earth. I'm gonna go out on a limb here and chalk it up to the "pilot left the cyclic friction on" cause. A lot of 206 pilots really like to crank the cyclic friction on while doing the runup for some reason. I've seen people forget it. "But you'd notice!" Would you? Maybe not. Depends on who did the runup and who was doing the takeoff.
It is curious that the first person out of the wreckage appears to be the guy who was sitting in the right-hand (i.e. PIC) seat. The *second* guy who gets out appears to be seated on the left-hand side and - strangely - he is wearing a helmet. Now, was *he* the PIC? And did he let the other guy sit right-seat and make the takeoff? I've seen accidents caused my weirder stuff.