If the cabin isn't sold out then requesting a seat number might not work - in your example somebody might want aisle seat 30B and they could offer aisle seat 31B instead of 30B is taken. Why would they upgrade the passenger in 30B if 31B is empty (or move them back one row just so that somebody upgrading can have 30B).

And if the WTP cabin is already 100% full then the system normally picks who to upgrade by some algorithm - in your example the upgrader said "bulkhead aisle" which is four possible seats - so it's possible the algorithm would have picked one of those passengers anyway. And if it didn't it's hard to know if his request for a bulkhead aisle is turned down and something else offered or if this influences the algorithm and somebody is upgraded to CW who would not be at the top of the list.