There’s what you have in you stomach and intestines in transit along with the water associated with that…then there is the glycogen you will have replenished and the water associated with that. Personally, it sounds like you are in a really good place regarding just how much body fat you have dropped. Well done and I hope you see the positive as I do.
The heavier you are the more water weight your body holds. At 450 lbs I’d wager 15 of those lbs is water weight (total guess). I understand it’s discouraging, water weight is misleading, but the bright side is YOU LOST 50 POUNDS!
The weight is from the food in your stomach, intestines, etc. And also, you eat carbs, so you hold more water.
This is not fat being put back on (where could it come from?). Also, measure yourself. When the scale won’t drop, usually your measurements are.
Muscle weight is heavier that fat.
You are doing great! Keep it up.