I suspect its another unscientific poll conducted by crew commuting home on Iberia. The other places are full of these things, like "70% OF CREW WENT ON STRIKE", based on a militant trooping round the aircraft demanding to know who'd been on strike. It doesn't seem to have occurred to them people might lie in order to get rid of them.
Anyway, does it really matter of 80% of them say they'll go on strike? BASSA tell us that 80+% of BA cabin crew will go on strike and the airline seems to run better without them.