If one is going to follow the Occam's Razor argument, then I would suggest that all the technical equipment was functioning perfectly. The helicopter was operating close to the limits of its' endurance and the pilot may well have expected fuel warning captions to start to operate. Confirmation bias led to the warnings being cancelled without fully taking in what they were indicating due to confirmation bias. The engines flaming out came as a complete shock to all concerned. Human error, late in the evening, after a longish deployment. The only thing anyone is thinking about is finishing the tasking and getting back on the ground for a welcome cuppa and a trip to the loo. Been there, done that, albeit at ground level.