I think I would be having a much closer look at the bend in the spokes to see if there is any damage to the coating -- that, and have a look at the fork. If, as you say, there were branches on the roadway, there is a chance you flicked one into your spokes.

I don't see much of a taper, if any, on the nipples where they would rest inside the rim. What you see as taper, I think, is just the normal shape of the nipple where it goes from round to flats for the wrench, and they wouldn't have any influence on the integrity of the rim.

The fact that there ISN'T any taper on the seating surface might be a clue to what happened, though.