[curtains]

He has ace high, there is a reasonable chance its good. There is a lot of money in the pot, if there is even a 25% chance he will win against the lone allin player, its probably in his interest to knock out the other guy from the pot.
He really doesn't care at all about knocking out the other player with his chip situation. What he cares about is maximizing his chances to win the pot...and making a tiny bet did this.