Interesting. Usually a player switches like that when they don't stand a chance of playing for the stronger nation. However he has already featured pretty heavily at youth level.
Perhaps you're right, it does seem like on the face of it he is being patriotic. Plus he must be getting nice money at Leipzig, so money is not a driving factor.
However England have a very poor history at choosing players who play abroad, so maybe he felt like he's being overlooked.