Are there other gated access roads similar to yours in the area? Because the vibe I get is, this guy wasn't a hunter or even a local. He may have been given instructions to pick something up. Something like this :The (money, drugs, guns, morel mushrooms, whatever) are in a brown paper bag. Go about x miles down "whatever" road until you see a red gate on your right (or left). Walk down that trail xxx yards and you'll see the bag lying next to a big stump." Now, hes' not dressed for scouting, but he has jeans on...like he knows he's gonna be in the woods...even tho it is clearly hot enough to be wearing shorts. He's only in there 2 minutes and comes out empty handed. If he's not familiar with the area and there are other similar access roads with similar gates around, he could have just been in the wrong place. To me, it looks like he doesn't know he's being photographed. This may speak to the quality of your camera (it takes pictures without any visible flash or audible noise) OR he is not outdoor savvy and doesn't know that trailcams exist, or how they work. He isn't looking for a new hunting spot, or scouting. When was the last time you went scouting with sneakers on and no hat? He just made a wrong turn looking for his "pickup". The fact that your gate has posted signs on it, and he ignored them, would tend to point towards something underhanded going on. But, if I had to pick up a 10000 dollar shipment of cocaine, or I was looking for a clandestine meth lab, I doubt a posted sign would give me pause. Maybe he got down your trail a little way past your camera, and realized that whatever he was looking for was not in this particular place. So, then he turns around and goes back to the main road to look for other gated access roads nearby. If this was the case (that is, he was a bag man for some "transaction") I doubt you'll ever see him again. The fact that local police and postal workers dont recognize him would seem to support this.
Of course, this is all speculation. Let us know how it works out.