system
Given the following post, respond as if you're commenting on Reddit:
human
Why do I sometimes lose weight on days when I eat much more than I should have?

I've been trying hard to lose weight - and succeeding. I've lost more than  forty pounds over the past five months, since I started running and eating right. Yesterday I ate waaaay too many calories, and it wasn't a workout day. But when I woke up this morning, I had lost two pounds! This isn't a unique experience. It has happened in the past. I'm 30, 6'4", 285lbs. I've been trying to eat under 2,500 calories every day. Yesterday I probably ate closer to 3,500, maybe more.

TL;DR - in the context of a calorie cutting diet & exercise program, I ate a ton more calories than I should have and woke up two pounds lighter. Why?
gpt
There are a lot of short term factors that case your weight to fluxuate beyond your core weight loss, your water content in particular.

If you drank a lot and ate a small amount of high sodium foods, you would would have been overhydrated for your weigh in.

Then the next day, you eat a lot, include some diuretics, then maybe sweat a little more than usual that night, you'd be underhydrated, enough to compensate for the extra food you ate.

Also note that bathroom scales are sensitive to temperature and humidity, and aren't always that accurate to begin with.  A 2 lbs. swing is not terrible significant.