Just looking at the layout of the airport... that is a gotcha which has happened elsewhere as well to much more experienced folks...
If I get it from Airbubba's message, then it is not untypical what happened here.
Big Runway 20R, Small runway 20L and parallel TWY.
You know you need to go to the left runway which is smaller than the right one, for some reason fix on the right one and then think oh, hang on, need to go left again.
Happened to a BAC 111 at Gatwick many moons ago, BIA if I am not mistaken and scared the bejazis out of an opposite 737.
By the looks of it he must have seen the 737 and avoided it easily enough just wondering what the heck it was doing there instead of getting the idea that he was in the wrong place. One of these incidents where a flat forehead may well result in aftermath.
Well, nobody was hurt and wasn't likely to be hurt either. And if Harrison is a nice guy (which he is I understand) he'll write a nice "I learnt about flying from that" for all of us to help us understand why it happened so we can all learn from it.