Kinsler lets the ball drop in order to switch runners on first base from the fast guy to the slow guy.
I listened to all 4 announcer groups (2 TV, 2 Radio) and 3 of them got it wrong at first, only the Detriot radio announcers knew it was a legal play and applauded him right away, the rest of them somehow didn't know the infield fly rule required 2 runners on base.