ML/NJ
Having analyzed many dam break scenarious in my younger days, I buy it just fine.
Ice dams break quite suddenly and, although "in an instant" may be a bit of a hyperbole, a 24 to 48 hour time period is quite possible given the volume and the distances that the floods traveled.
For living things in the lowermost one fourth of the flood path, that is a distinction without a practical difference.
Animals were sensing the P waves from the earthquake and the tsunami’s interaction with the sea floor, both of which moved much faster than the tsunami waves. I’ve never heard of any seismic waves associated with ice dam failures, let alone any species that would have it genetically programmed to respond to ice dam failure seismic waves.