Well it doesn't sound likely that this would happen and looking at this logically, the only way it could happen is if you are taking so much Proviron that it is crushing your estro too much but that just doesn't seem likely. I am not a chemist or a doctor so I can't back that claim. Furthermore, your "friend" said that his penis is smaller and cold to the touch which would suggest that there is some kind of imparment of blood flow to his member. THAT is a bad sign if this is true because as we all know, if your arteries are clogged in your genitilia, to the point where ED is happening, you might be having some some arterial blockage in other areas as well, namely your heart.
Either way, that is some scary shit so I'd tell your bud to go the doctor and get some bloodwork done to see what is going on.
Good luck!