They probably did. Things that sporulate (bacteria and fungi) are very difficult to "winterkill", at least in the same sense as plants are killed by cold weather. In
this reference, cryopreservation was tried on some arbuscular mycorrhizal fungi and the lethal temperature that did them in was -180C. Cryopreservation at -100C was successful, and while it may have felt like it, the polar vortex was nowhere near that cold.
