I agree with the other posts. It appears the poor trucker who now has to live with this was just traveling down the road. The only thing the trucker may have done is if a retread got thrown but there is none that shows in the pictures. Looking at the pictures, it isn't much of a curve. It does look like some loose gravel in the first picture perhaps.
Either the rider was riding too fast, beyond his/her depth, fixated on the truck, hit something in the road to loose control, mechanical failure of the bike or something physical happened to him/her prior to the crash - passing out, heart condition...whatever.
Looks like rider error or bike mechanical failure to me.
Doesn't really matter though - shame to loose a fellow biker - no matter what the cause.
