My dad had a similar experience hunting in Iowa. He was using my slug gun since his scope is actually a rifle scope so the reliefe puts it too close to his eye for comfortsake. I had left some ammunition in the blind to cut down on weight for the hike so he didn't bring any extra and forgot to load the gun. Fortunately he had his .44 super redhawk with so it was no problem to put down the shotgun and grab the pistol when he and my sister jumped some deer. He put the shotgun down on a backpack on the private property we had permission to hunt on and tried to circle around. They didn't get any shots off so my dad headed back to the truck and my shotgun. Except the shotgun wasn't there but the backpack was.
So he walks around looking on the ground, looking around the truck but couldn't find it. So he hears some people talking down a hill over the property line. Comes up to a group of people who are just leaving and asked if anyone had been up by the hog house where the gun was. Some guys in one van said "nope, been down here all day."
He kinda glanced around inside but didn't see the gun in plain sight. So he asks the guy at the next and last truck and he says "Hang on let me make a call."
So he calls someone and says "hey did you guys find a gun while you were up by the hog house? ... you did? ... Well there is a guy here who wants it back."
The white van comes back and the guys were lookin a little guilty. Turns out one guy was smart enough to put it in his gun case to hide it from the other honest guy and has his shotgun disassembled between his knees. So I got my Mossy 500 back and none the worse for wear (thank god)