Moffat posted regularly on the old Outpost Gallifrey forum, sometimes commenting on the show, sometimes joining the discussions, just like the rest of us. Outpost Gallifrey was the major fandom spot when the new show started. They went to the biggest Doctor Who Con both as guest and as fans for years.

They wrote fanfic and later they were part of the group that wrote the books and audios, which are basically professionally published fanfic. So I think they were just as much in the fandom as we all are and they just had enough talent to make it big.