If I was a betting man, I would say the investigators will find out that he was regularly flying a Dash-8 on a computer flight simulator, such as a later version of Microsoft Flight Simulator or something similar.
You would be surprised at how detailed and accurate and interactive the cockpits are and also how accurate the startup, taxiing, takeoff, cruise, descent and landing procedures are with those simulators.
It will be interesting to read the final Probable Cause report from the NTSB in a couple of years or so.
Edit to add:
I found it interesting that he was surprised at the rate of fuel consumption he noticed while talking to ATC. He seemed to think that 3000 lbs of fuel was enough for him to fly around a long time.
If my flight simulator theory is correct, then that possibly tells me that when he flew the simulator, he could have been doing so with an unlimited fuel setting.
Also, he may have never paid attention to how many pounds of fuel would be evident if the tanks were topped off or filled to the capacity that proper weight and balance would allow.
Not to mention that he could have advanced the throttles to maximum power at takeoff and left them there and who knows how the props we're configured.
Also, I don't think his altitude was ever near the cruise altitude of that aircraft so I would think that would have a negative effect on the fuel consumption that he was surprised to observe.