I would think that most of the weight loss would be water weight. The problem is that if you are working hard and sweat a considerable amount, you can easily sweat more than your gut can absorb.
What I do in that situation is just drink water for awhile after the ride until I "catch up".
I doubt very much if the loss was the result of burning calories. It takes 3500 calories to burn a lb of fat. I figure to burn a lb of fat, I have to ride about 70 miles. Also in order to burn the lb of fat, I can not take in any extra calories as a consequence of my exercising (which just is not going to happen). I have lost weight by exercising long and hard but it is more difficult than one would think. One has to exercise quite a bit and one has to be restrained on the food intake side of the equation also.
In your case, I suspect the 32 oz of orange juice more than made up for the calories you burned during teh ride. Orange juice tends to be loaded with sugar.