Yeah, I'm not sold on the spotters claim given it was night time. And, at 6.7 miles one way you'd need a spotter about every mile if seeing conditions are perfect but at night how could that be? I've done some longer flights in the daytime and in remote areas but nothing near 6.7 miles.
I can see my drone out to about half a mile or a bit more if conditions are good but if I take my eyes off it at that distance to look at my FPV screen I am seldom able to reacquire it so I find it dubious that your spotters were able to see it at all unless it flew right over there heads and even then it's more likely they heard but didn't see it.
Lastly, the screen shots show you were flying near built up areas where a helicopter flying low is not out of the question. I'd recommend NOT posting the video to YouTube as the FAA tends to frown on such things and you don't want to be made an example.
Brian