No one has commented on the witness, my helmet or the front wheel & tyre.
I estimate the impact speed at 12-15mph.
I'm not aware of any kerbs, ledges or stumps though I might go and check.
I'm not saying that carbon is inferior to steel, just different.
I attribute "Then we can clean up behind you" to a lack of education.
I didn't cry but was rather shocked.
The car driver/witness was charming and gave me and the bike a lift home.
If minds remain open then we might all learn from this...