Gordon Shumway: Well it is 5 points for a backgammon win.

When a person times out, the computer checks for the worse possible position you could be in if the game went on. (not the position of the pieces when the game times out to prevent people from cheating and purposely timing out to avoid a lose at a worse position)

I'm guessing the computer checks to see if you have a piece moved out yet, which you did not - so decided that the worse position would be a backgammon lose.

Even though looking at the position it is obvious that you would have never lost as a backgammon - or even gammon, but the computer is not setup to check like that.