I often check out other people's computers and see the same thing - the map editor is open during games. Maybe the person is looking at previous replays or the current game. :)
You must be checking the wrong computers. By the way, in Wargame: The Hundred Years' War, you can't even view a map with the anti-cheat enabled!
PS. TOH was the coolest structure for many years! (at least 5 years)