I would actually like to think I'm somewhat of an expert on this.
In Highschool I wrestled, and throughout my 20's I competed in Wrestling, BJJ, Muay Thai fighting in various promotions from NAGA to Friday night fights. Pretty much I spent 15 years of my life "making weight" so I can say that losing 15 lbs of water weight is practically nothing.
Almost wish I could go back and do it again with all the knowledge I have on nutrtition today. People do not realize how much your body weight can vary from day to day based on your diet, and even from morning to evening. Try cleaning up your diet, load up on some potassium after two days and weigh yourself in the morning.
People forget the human body is mostly water, and water stores in fat and muscle so even at a lower BF% a man who is 6'2 and weighs 210 (what he's listed, maybe he walked in two days later and was 225) should be able to lose that weight after a few days of being sick, if he's dehydrated and hasn't eaten a lot.
Now, if that all muscle he lost in such a short amount of time, I would be insanely worried. Very worried. But I think it's pretty much impossible to lose that much muscle mass in such a short period of time.