OK, we covered this in an earlier thread, but I'll summarize quickly:
The "thrown backward" you reference is something which needs clarification. I agree that a person's head and shoulders would be thrown backward, provided the point of impact actually impacts the rider's body at a low enough center of gravity, IE below the body's natural fulcrum point. I've used the comparison of a football wide receiver catching a ball above his head, and then being hit from behind at a point below his waist. His torso flies backward, his feet fly forward. But relative to the spot on the field where he is hit, he does not move backward (in the direction from which the tackler came).
Same with a vehicle. X--------->>-----Y--->>-----------Z
(Arrows represent directions of travel for both the vehicle and the bike.) If "Y" represents the point of impact on the ground/street, then it is virtually impossible for the rider to fly backward toward and land closer to "X" than he/she was at the point of impact, assuming the bike is hit from behind. The head and torso may lunge in a backward motion as the feet fly forward, as we have covered. But the cyclist at point "Y" will, at the very worst, land at a spot which is parallel (to the side of) "Y".
All opinions and contributions are welcome, including dissenting opinions and analysis. Iron sharpens iron, and all that jazz.
There could be blood. Or debris from the bike. Or scratch marks/scars on the pavement from there the bike was dragged (even if only slightly) upon impact. Or all of the above. It's not a hard, fast rule which says at least one of the above would be present, but the odds are highly in favor of there being some sort of evidence of a crash between a cyclist and a vehicle at or near the point where the rider and/or the bike crash to the ground...even if not visible to the naked eye. When metal rubs against concrete or asphalt, abrasion occurs. The evidence left behind may only be in the form of small metal filings, rubber, etc., but something is bound to be left behind, you can rest assured.