Crew hours, aircraft availability, stand availability could all be symptoms of the delay but the initial cause was almost certainly the severe and sustained CB activity from 1130 onwards.
Harry, it's not beyond the realms of possibility that crew hours were a secondary cause here.
Or that there was a new shift on duty which hadn't experienced the worst of the weather and weren't completely aware of the earlier disruption.
That would certainly fit with the first person saying 'crew hours' (which may have been the knock on effect) and that then being corrected to weather or ATC (primary cause).
But since Gatwick was scheduled to around 95% capacity that day and only managed a movement rate of about 50% for 2/3 hours there was significant disruption and cancellations across the network for the rest of that day.