I looked it up and saw it, as well. It seems to me that he is winking, and you can tell that LBJ is smiling (even though you can't see the front of his face, you can tell that he is smiling because of the way the side of his face look, if that makes sense). What does it prove? Nothing, really. Nothing at all. Yes, "high fives" would be out of place, for sure.
As for conspiracies in general, I find many to be unconvincing but all are fascinating. But if you are taking the position that all are "crap," I believe you are wrong. I believe in a bare few of them, and a plot to kill JFK is one, for sure. Cuban exiles and Mafia types, in particular, had good reason to participate in the plot to kill JFK.
Come on. Post your best evidence that makes it "for sure." The Conspiracy Industry can't even decide if it was Nixon, LBJ, The Mafia, Castro, the FBI, CIA, the South Vietnamese or some husband of a broad that Kennedy shagged. But they're all "sure" that there was a plot.
The only things I am sure of is that any conspiracy that involves more than two people will never stay secret, and that the Warren Commission report fits all of the facts available --- then or now. People have been shooting at it for over 40 years, and no one has yet demonstrated that it is wrong on any of its material conclusions.
I have seen no evidence to make me "sure" of anything other than publishing conspiracy theories can be 'fun and profitable' no matter how far out they are. There is a market of suckers who will buy them.
Whether there was a conspiracy to kill JFK or not, LBJ's reaction is immaterial. If we heard today or tomorrow that B.J. Clinton or Ted "The Hero of Chappaquiddick" Kennedy was assassinated, don't you think it possible, or even likely that some of us might smile or wink? That would not mean we were involved, mind you.