I think the minimum raise on the river is the clearest piece of information in the hand and narrows his range to just five possibilities.
He is the current CL and doesn't want to loose that status anytime soon. He really doesn't want to go down to the felt in his first hand at the table. Flushy feels the same pre-flop...
..obviously the only man i was worried about was the CL, of course poker is a bitch so they all pass except the CL who flat calls the 12k more
So if you accept that this guy feels really strongly about his position it is clear that his river action to AT LEAST pot commit his opponent to a showdown, if not induce him to come over the top for more chips, would indicate a very strong hand. With his opponent presenting a massive danger he never does this without huge strength imo. This high risk move, and the fact he starts pumping chips when the A arrives, would point to of the very best of that 5 hand range and so it makes the straight the most likely scenario.
Of course, we know from the result that his min raise was a mistake....namely pushing the 5th nuts hand against the 3rd chip leader....the same mistake we make by pushing the 4th nuts against the CL. I think both hands are being overvalued in the face of such potentially crippling danger...the "most of the time" theory is ok when your opponent has less chips or you need to take that sort of chance (which is most of the time) but not in these circumstances. While he may have one of the two hands we beat from his range....I wouldn't bet my life on it...so calling to showdown for a massive pot is the best play.