The picture is part of the tweet, but it doesn't say "So long suckers, you chose the other path!"
He doesn't say "if you'd followed his messianic advice/example you too would be diving on a coral reef somewhere".
About the first point--I didn't take that to mean it was part of Garner's tweet but rather @FMM1's interpretation of the implied message--in other words, it was commentary. It wasn't intended to be read, I don't think, as being what he said literally. However, I agree that could have been made clearer in the tweet.
The second point--about his messianic example--is clearly commentary and seems pretty hard to dispute by saying "he didn't say that." No one would read it and think he himself said it literally. But it certainly seems like a fair interpretation of Garner's position. He might or might not actually feel that way, but that's the impression many reasonable people would have to what he lays out.