Rubik101, since I know the smell of heated de-icing agents from 5 years of volunteering at the national airport, I'd probably identify that smell quite quickly.
Perhaps it would help if Ryanair would invest in some actually fire training so their people can tell the difference between electrical fire smoke, gasoline based fire smoke and de-icing fumes.
Regardless, it's not me you need to vent your indignation to. The Ryanair TRAINING DEPARTMENT states that evacuation in cases where no uncontained fire is obvious (fire outside the fire cages of the APU or engines) or where the structural integrity of the aircraft is obviously sound, evacuation is not recommended.