The first screenshot is the bus stop today. The stop has been moved 50 yards closer to Forest Road in the direction of Walthamstow/Leyton stone.Maybe he was deciding whether to call it in, or just leave it for someone else to report, and after a minute or two his conscience got the better of him?
The second screenshot is where the bus stop and phone box was in 1996.
The third is from Crimewatch 1996 showing the phone box and bus stop at night, at 2A Fulbourne Road.
I like your theory of the driver's conscience troubling him and thus stopping to make the call but I am more inclined to think that since he was travelling in the Chingford direction, moo, that that was the first available phone box that he saw.
Very difficult to get into the driver's mindset here.
EBM.