Most likely he wasn't completely empty when you weighed him the first time.
I have a male that finally broke his fast last weekend, his last meal before that was October 8, 2013.
A few weeks before eating he pooped for the first time since last year. Yes, he digested that last meal (or few meals) from last fall over the course of several months.
Yours has been fasting for about two months and has lost 65 grams. I wouldn't worry yet.