Quick crash course on CRJ electrical system:
2 AC busses are powered by the engine generators or APU or ground power. In the event that the aircraft is in the air (ie not weight-on-wheels) and both AC busses lose power, the ADG (Air Driven Generator, as it is called) automatically deploys and powers the AC Essential Bus as well as the Hydraulic 3B pump. This will give enough instrumentation and systems to bring the aircraft to a safe landing somewhere.
My guess here is they had the FLAPS FAIL caution message, completely ignored any QRH procedures, were distracted and landed with the gear up, thinking the GPWS warnings were for the flaps and not the gear. Obviously there was no Weight-on-wheels on the ground, and when they shut the engines down, the ADG popped due to the WOW switch still showing airborne.