Either you moved more then you think or something else drew their attention to you. It is highly unlikely that they picked you out from 80 yards away for no reason. Even if your camo is bad your outline would be tough to pick up from 80 yards away.....unless you were standing out in the open which you obviously were not.

It is very possible that the deer saw you a long time before you saw them......maybe they just stepped out to get a better look at you after watching you for a few minutes.

You never know when a set of eyes could be on you.......even if you see nothing.