I was struck in the leftcenter chest on 10/15. By dec 27 test found to have multiple bilateral pe w/factor v, timing right for 10/15 injury as cause?

Hard to know. Factor v leiden (inherited from one or both parents) increases your risk for clots in the legs that can travel up to the lungs, where they can be lethal. If your chest injury made you immobile for a period of time, i.e., days or weeks, you may have developed a leg clot that traveled northward. But the injury may have had nothing to do with the pe! Could a recent plane flight have put you at risk?
PE. Chest trauma can certainly be a risk factor for a pe, but usually soon after, and it is really not possible to prove months after if there was any casual relationship. Not to mention, an underlying, since diagnosed factor v deficiency would not be related to the trauma, and would be the main risk factor for clotting disorders. Best wishes.