Could my friend have an eating disorder?

He's 18 years old and has been in hospital a few times recently, this was one of the first signs I noticed, he was severly dehydrated. He also tends to avoid situations where food is involved, if I ask him to come out for the day he will make excuses about that he can't come out until after 12, today I managed to get him on the scales, he is 5 foot 7 inches and weighed 124.5lbs, you can see his collar bones and ribs alot! But the weird thing is that in december he was overweight so he must have lost atleast 2 stone in the first month :/ I am really scared, he gets moody easily aswell :( what should I do? Do you think he could have an eating disorder? Thanks :)