It's the latter. Was on an AA flight from SFO and we were off loaded there once. Almost took longer to deplane, wait for the buses, load the bus, and drive to T4 then the whole flight SFO-LAX. This was of course during the T4 upgrade.
What a waste. Might as well use stairs to get inside the aircraft. Also could have used the same 'structures' for planes on both sides, including the KE 'crafts, with bridges going both ways, since I am assuming that these are not boarding gates where pax lounge, and that they are only used to board. Either way, a waste.