I agree. Moo, the hair is a complete non starter. Yes, from memory it had no root. I'm sure this was why it took such a lot of extra testing to even identify it. Jmo, but see testimony of Valier I believe, plus I haven't read it but this info may be in your link.
John could have shed it himself some time that day/evening as you say, in the normal course of events. It's also possible KR herself innocuously transferred it there at some point on Jan 29th after JO's passing. Moo
She did, afterall, lie on him in her grief and horror trying to warm him, before attempting CPR with Kerry Roberts. She could have picked up a hair on her own person, which later fell off her clothing onto the Lexus Moo
Given alternative and imo far more reasonable explanations for the hair, I find CW's push for it being unassailable evidence of an impact, just like the presence of touch DNA but with no accompanying blood or skin (zero, none, zilch) underwhelming to put it mildly. Laughable to put it less mildly. Jmo