That is surprising and commendable as well from the admin, i thought this sort of request usually takes a bit of time, or even outright rejection most of the time. I guess this is your second change of name mate, if you do not mind can you tell us how long it took the admin to accept your request in the first instance and how long it took this time around.
Highly circumstantial I imagine. If there's a legitimate reason to change a username, and theymos agrees that, I imagine he's more inclined to do it. Although, timing could be hit, and miss. Might have just caught them at a good time. Although, most of my communication with theymos has been relatively quick. Although, I wouldn't base how quick it too this time around or my experience with theymos. If you ever wanted to change your username, you ask, and it either gets rejected or takes as long as it takes.