I will bet: they turn the pilot off, close off the inlet, hook up a hose and drain it. Followed by one or two 'flushes' by opening the inlet. Once it is full and ready, run a 'mixture' of hot and cold water to all faucets to help flush those lines out. I did this on my own last year after sediment deposits and brown water created air pockets in the (hot) water heater. It did the trick, and of course removed the bad smell.
I will also bet that it was hooked up, briefly tested, and the maintenance crew was on their way immediately.