It's basically how many times he's willing to make what should be an extremely risky bet. Normally that kind of play would be reckless and exploited by the other players, but for some reason it almost always works out for this guy.
No that's not what the graph shows at all. It's just his win rate in terms of how many big blinds he's won per 100 hands played, against the percentage of hands he's choosing to play.
