If the Capt was called out to operate the flight at the last minute , in order to save time one would assume that he went directly to the aircraft from the AEL
Stopping for a coffee would take no more than 5 mins and presumably give him a much needed caffine boost for the flight , after being on reserve for a number of hours with no chance of achieving pre flight rest, because he was unaware that he was to be called out for a long haul flight
Personally I think it was a very sensible decision to arrive at the gate in a calm professional manner instead of looking flustered and harried
It really is falling apart isn't it