I think it was a crater from a fragment that vaporized off of it. If i'm not mistaken, it blew in the upper atmosphere, leaving no impact crater.
IMO, it's interesting that the angle of impact is thought to be that much of a glancing blow. Several previous studies of the tree damage have suggested that the angle of travel was very much like the crater pattern they found in the lake. It will be interesting to see if they actually find a core.
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