Butler made all three free throws to give the Heat a 103-102 lead, but the Celtics still had three seconds to attempt a game-winner. They inbounded the ball to Marcus Smart after the initial action was blown up by the Heat, and Smart quickly fired the ball at the rim. His shot almost went in, but it popped out right next to the rim, and White was right there to deftly flip it up and in at the buzzer. White did so just in time, releasing the ball with 0.1 seconds remaining.
This is where we go back to the officials' decision to put three seconds on the clock. When you go frame by frame, Horford still hasn't made contact at 3.0 and it appears the foul doesn't happen until 2.8 seconds left. It's unclear if the refs had a different angle, but it seems as though it should have been reset to 2.8 seconds. That, of course, would have meant that White's tip-in came after the buzzer.