From what I remember, if they don't have enough 'single' rooms they often allocate norfolk and suffolk twin rooms to only one person, then charge them the normal single rate.
I'm not saying this is definitely what has happened here, by any means (so don't get too hopeful) but it definitely happens, since I got told by someone on the open day that the twin room in their flat was like that.
If however he is sharing, try to look on the bright side. He gets the same bathroom and kitchen facilities as everyone else in the flat, the beds are divided, so it's almost sort of like having a separate room and you may make a really good friend through it. When it comes to say, him having you staying over, I'm sure that every now and then they could sleep around a friend's flat to give the other some privacy. And it will be sooooooo much cheaper, to the extent that if you really wanted you could use the extra money to rent a travelodge room every now and then
If you are really unhappy with your room placement, you can go when you arrive to talk to the office, and they will put you on a list. Then they will try and find a room for you when one frees up (prioritising based on the reason for changing). I know a friend who got changed from village to en-suite campus a couple of weeks in, because he didn't get on very well with his flat mates and was feeling a bit alone in his flat. As people move around, more rooms free up throughout the year. It may be worth emailing them beforehand, I would imagine financial reasons would be the most 'important' reason for changing but they do consider everyone I think
but also, you could just pop in once you arrive- hopefully UEAAccommodation can clarify whether or not to email or wait.
The last paragraph above also applies to you.
xxx