It's not a smooth wall. I don't know why anyone would write on it believing it was a whiteboard. This is why I'm not surprised that they used pen that didn't come off: people who are unthinking in one dimension tend to be unthinking in most other dimensions, too.
At least they didn't write on the projector screen, which someone has done in the room (1NW.4.1) where we had the Educational Away Day yesterday. Then again, at least that room has a projector screen, unlike the other room I teach in, 6.345, which projects on and around a whiteboard which has been used so much it's basically a ghostly palimpsest of years of previous lectures.
We're getting a smart whiteboard in one of the labs soon. I daren't imagine what non-smart people will do to it.