That doesn't make sense. Maybe the scale is off or it's water weight and not fat. I hope he doesn't become discouraged by that and continues for his health.
I know, it's really weird. Maybe it's his body adjusting in some way but I'm sure it will all even out soon. Luckily it's not discouraged him at all. He is always having phases but I think he is actually going to stick at this, he seems so dedicated!