Poor guy - definitely embarrassing. I speculate he's never used an AR15 or never used an AR15 with that sight. He's just unfamiliar that he doesn't even recognize that it is on backwards.
Sage, what are your thoughts on the Mossie Tactics FSB light mount?
I ran a kind of similar mount for a while. You'll want a tape switch for it, but it's not a bad place to put a light IMO. Shadows aren't really a problem with lights that are on top of the rifle. You might get a shadow on the target's groin or something, but do you really want to look there that bad?
I think the one I had was a CAA. It mounted through the A frame, with a rail on one side for a light. With a modern "hand as far forward as you can without putting a bullet through it" hold on the rifle, it worked great.