Hard to know for sure, but I'm leaning towards the guy being an a-hole. Or, being completely f'ing thoughtless, at best. For all he knows, you're a veteran with PTSD (I gather that PTSD causes "hypervigilance"). There's all kinds possible of reasons to react that way.
I recall an article by a vet with PTSD, who, due to some gunfire in the movie, dove down onto the theater floor and ended up covered with popcorn. I image if someone had laughed, his wife (who was there) would've verbally ripped them a new poop-chute.
It seems like people tend to interpret almost everything anyone does as a deliberate social message to the person watching. It's as if there is no such thing as actually being in pain or accidentally falling down. Everything is somehow a deliberate pantomime, and actual reality isn't the important part. Or, maybe that's the assumption when the observer's experience doesn't match up with what they're seeing someone else experience (failure of empathy?).
So, covering one's ears or cringing from loud bells doesn't mean, "I'm in pain," it means, "oh look, look! I'm pantomiming that I'm in pain because I want everyone to see and acknowledge it! Look! Look!"
Or something like that. I could be wrong.
Anyway, what happened in that store sucks (and what CR talked about; that also sucks when people do that).