I don't think it's hard at all to imagine there being a concussion, much less is there any basis to call him soft.
It's not just the initial contact with the sternum--which is definitely enough in and of itself to cause a concussion--but the possible second impact when the head snaps back and the brain hits the other side of the skull.
I do think a lot of people are pretty ignorant about how concussions happen.
As
@HuskyPride87 notes, he either has one or he doesn't and it won't be his choice about how long he is out. If he has symptoms, he won't play.
He could also be fine.