Buses.
To answer the question the bus pick up road is run one way. This means inbound buses from the eastern apron have to use the road that crosses behind stands 1 2 and 3. There is no problem when the aircraft are on stand but the delay in question may have been whilst an aircraft was in the process of push back from one of these stands which would obviously close the road for a minute or two at the most. Not a huge problem unless you chose not to pay mr o'leary for the use of his toilet !