Coyotes get called a lot in Revere, so it could be that they finally heard the call and remembered the bad experience they had last time when they heard that sound or they winded you or saw movement.
Shiny objects can make them turn and run, but I would bet they caught wind or movement. On the other hand, it sometimes amazes me just how much movement one can get away with while on a stand.
This past Sunday I was hunting and accidentally knocked my rifle over on to the rocks, it made a hell of a clatter. My e-caller was going like crazy and here I am banging the AR around on rocks. Not two minutes later comes a nice big coyote to within 35 yards of me focused only on the caller, I was caught completely off guard. I was moving around trying to stay comfortable sitting on a rock and my caller was just 5 feet to my right which was a big mistake. He didn't seem to care about anything but the sounds and I kept turning around watching him as he came closer. Finally he caught wind and turned to leave but was in no real hurry, appearently he never saw my movement and I was sitting in the wide open. So I shot him at just over 300 yards when he stopped to take a look.
If you think the shiny barrel is the culprit, just wrap it with some green vet wrap or horse wrap, that will cover and protect the barrel during your hunt and removes easily with no residue.
The lens covers that prevent reflection is used primarily for low light conditions when using a lighted reticle in military or LEO covert ops. It probably couldn't hurt but but I would try the vet wrap first and work the wind.