Sorry to be picky SASless but according to the report published by CBC, zero pressure has been lost at 5740 feet not 800, which in my view highlight even more your questionning:
12:17:42 CHI advises Gander ACC that they have lost all main gearbox oil pressure. CHI91 is descending through an altitude of 5,740 feet.
Back of what you say I agree, and the following months will tell us a lot more.
FH