He said he felt it. Small cuts are usually felt. It is not like a bullet wound that destroys the surrounding nerves so rapidly that the nerves do not send any pain signal. Bullet wounds are often not felt as pain but as loss of function.
Why you might not feel pain until you notice a cut (
Link )
He may have used the word incorrectly, but usually concussion means some kind of an impact.
When it impacts a body. That person has a "concussion".
So I don't know how a 'concussion' could be sensed from anything other than the impact of the shot.
Post-event ...
Merriam-Webster
2: agitation, shaking
The concussion from the explosion was felt 12 miles away.
Collins
2: any violent shaking; jarring
He said:
"but I kind of got, by turning around, I don't know whether I got a little concussion of it, maybe when it hit something or not, I may have gotten a little concussion that made me think there was something different to it."
He's being asked about the specifics of the sound: "Describe as best you can the types of sound of the second report, as distinguished from the first noise which you said was similar to a motorcycle backfire?"
Because, after hearing the second shot, he had turned his head (
ie: it was oriented differently than it was with respect to the other shots) he thought the position of his head might be why he thought the reverberation of the second shot sounded different. He also offered that the difference may have been from the shot having hit something. Either way, it seems to me that Greer is taking about the sound properties of the reverberation.
It is not very clear exactly what he was really saying but it does seem that he thought he sensed some kind of an impact.
That might explain why he thought the repercussion of the second shot was different. He also said it could have been because he turned his head around and was hearing the repercussion.
His reference to turning around, which he said he did immediately after that second shot, may indicate that it took half a second to fully register.
Except that he said he sensed the concussion on the second shot and Tague said he was hit on the second shot.
One's a description of the reverberation and the other's a perception of when the pain of a minor nick was perceived. If you think those things somehow solidly connect to the strikes to the windshield and frame, well OK.