The controller(s) may well have been considering doing a vectored "hold" but were able to turn them back toward SFO earlier. It is quite rare to get an actual hold, published or unpublished, for anything other than practice in the US. If you do, it is because you are heading somewhere that had their acceptance rate take a dive and may have different direction flow. SAN gets this when they have to switch to Runway 9 for the ILS. That is one of the few time I'll see stacks of holds - to the north over Santa Catalina and east seems to either be over IPL or using a fix.