I watched him yesterday for the first time, as he was winning #24. He does a couple of strategies that are contrary to Jeopardy custom: all-or-nothing wagers on Daily Doubles and starting with the hardest and highest-value questions. He also just knows a whole lot. Between getting the first few $1,000 responses correct and then winning a true daily double, he was way ahead before the other two contestants had even gotten their feet on the ground.
Another thing he seems to do well is time the clicker. About a decade ago, a Baylor student I knew went on College Jeopardy. His report: he struggled because he couldn't get the timing right for when to click in. If you click before Alex is finished, you are locked out for a few seconds while others have the chance to buzz in. So the key is to anticipate accurately when the signal light will come on telling you that you may respond. (It doesn't come on until Alex has finished reading the "answer.")
He also seems to have an ability to instantaneously do mental math (or create the appearance that he does). His Daily Double bets in the second round were not all of his money, and they were weird amounts. I haven't watched enough to tell if there is method in his madness on Daily Double bets when he is way ahead.
Anyway, it was an impressive performance, and he "only" won $86,000.