In all probability the rider at the back freaked out and grabbed everything when he saw that a collision was on the cards - clutch & both brakes which would make the front slam down as we saw - but of course, the front brake would not work until the wheel was on the ground and then STOPPIE!!..but it was too late. Interestingly, was there enough time and room to steer the rearmost bike around the front one? Probably yes, if the rider was not in panic mode...you often see this behaviour when people in cars with ABS get themselves into skid/collide situations - they just stomp on the brake and stop steering and wait for the cruch even though the ABS would enable them to steer round the obstruction if they kept control of the vehicle. I suppose the moral is to keep "riding" the bike to the very last moment - 'cos no one else is gonna do it for you!
Regards
Jan