Can anyone explain this???

Basically, your body does what it wants. There are more ways to retain water than just carbs. That day off from the gym and being more lenient with your diet was basically a break for you physically and mentally. This may have lowered your cortisol so it released some of the water.

Body chemistry is complicated. I've noticed that often I'll have a large dinner but be very slightly down in pounds the morning after. And the morning after that, the extra weight shows up. It seems out of order, as you'd expect that the literal extra weight from food waste would show up immediately but it doesn't.

Also there's a ton of variables - sodium, hormones, stress, illness, environment, weather, Jupiter passing the constellation of Orion. It's really hard to say, so it's best to wonder less and stick to it more!