Not sure why they diverted, unless they turned up just as SFO was reconfiguring for a change of runway and didn't have enough fuel to stick around for it. Checking later, SFO was landing on 19 and departing on 10. I noticed on the flight tracker for the repositioning flight that the 11 mile hop took 90 track miles.
I wonder if they hauled in extra fire cover - I know San Jose gets the local fire department on alert if a 747 is scheduled to land.