I think you are making a lot of assumptions here. Eg: It’s common for a ~200 lb male to lose 10 lbs (90 kg male to lose 4.5kg) of water weight in the first week or two. We don’t know anything else about OPs claim of weight loss over two months. We don’t know rate, overall starting point, level of activity, etc. This speaks more to the claim being ill-defined than of being a dangerous quantity.