Only after a sauna. It's the only time it feels nice for me, otherwise I'm not bloody doing it.
Also, there's no way a blast of cold water alters your metabolism enough to make you lose multiple pounds in one week.
As for losing weight during a week of excess eating, that's not unusual at all either. I tracked my weight daily for 5 years, and my weight consistently had a two week lag compared to my eating. So if I ate very little, I didn't see a loss until two weeks later. Or if I ate a ton, like over Christmas, I didn't see a gain until two weeks later.
Your body adjusts it's water levels constantly, so these types of fluctuations and delays are not unusual.
Basically, don't read too much into the weight change. It didn't come from cold water, and even if it somehow did, it would probably be a change in water retention if the cold water was somehow affecting your lymphatic system.