Some have asked why the penalty did not necessitate a 10-second clock runoff.
The answer is simpler to understand than the reasoning behind the rule. Basically, penalties for illegal motion do not stop the clock. In this case, the Dolphins spiked the ball right after the motion penalty. While the penalty negates the play for statistical purposes, it does not negate the result of the play, which was a spiked pass and automatic clock stoppage.
Had the Dolphins been guilty of a false start, that penalty would have stopped the clock, in which case the penalty would have given Miami an advantage, in which case two things could have happened. Officials could have run 10 seconds off the clock, or the Dolphins could have elected to burn their final timeout.
As things worked out, the Dolphins took the penalty. They saved their timeout and had plenty of time to run down the clock before attempting the winning field goal.