I considered carrying a crop for a moment and giving him a nice little "smack" but not chasing him when he turns around, but I can see where that will lead to him walking away as soon as he sees me pull up rather than waiting until I'm actually in the pasture and within about 5 feet. I know it's all a game because, in the past, my strategy has been to immediately turn away from him and go towards my other horse when he turns away or even just go straight for my colt. When I do that, he decides he's interested in what's going on and comes over since I'm not "going for him", and after that, he won't turn away even when I do walk toward him. It's almost like he wants the attention, so he plays "hard to get" to get it. (However, this was not the case with my boarder - ever time she approached, even with hay, he turned away before she even had a chance of getting him)
As far as the herd thing, this does remind me about when he used to let me approach his sides and flank, and even come up with his nose and head, but would walk away as soon as I approached his shoulder because he knew he'd get the lead rope thrown around his neck.
I think he might really respond to clicker training, which I've done with my other horse but not this one since he was already trained when I purchased him. Maybe that'll appeal to him as a game he's excited to play. And when we do targeting, I usually train them to target my fist. I think maybe taking this approach and helping him be excited to work with me (like my other horse is since he was clicker trained from the beginning - he actually DROPS for the clicker and his attention is always on me, the complete opposite of this horse) will help him to meet me at the gate so that he'll be caught first (that's what my colt tries to do haha). Maybe, to get him to come to others, we could also play a clicker game to come when called. I know there's one where, once they've gotten to a certain point, you can even have more than one person stand in the arena/pasture and call him one at a time until he comes. They learn to respond to this just like any cue.