After watching and with hindsight I'll say, Yes should have been ruled a fumble. But on the flip side with how it played out with the ball carrier very nearly getting the ball back as he hits the ground I can see it being called possession and down, especially in real time. I would not call it maliciously bad, but yes a missed call.
Is there a full posting / recording of the game? With how it ended (Amazing 4th and long TD by X to take the lead late and then Manual TD as time expires to win) I would love to watch the last 5 minutes of this game.