That's one possibility, although it seems to me that it would be odd if the diversion was in fact "sudden". (Caveat: Only SLF speaking here, but I would expect that a fuel diversion would be planned from some way out as the need ought not to take anyone by surprise even if it had arisen during the flight.)
Another possible reason for a sudden diversion followed by a short ground stop would be a medical emergency on board, someone who would be better off if offloaded at a diversion airport than carried a few more hours to the scheduled destination.