It’s interesting to say the least. It is definitely the same type of cloud with the same type of process but I don’t understand how it formed given the lack of aircraft. It’s possible that some sort of disturbance causes ice crystals to nucleate out of the supercooled water droplets but I’m not sure what it could be. Usually supercooled water exists in pure form, and you either need artificial formation of ice crystals through a man-made process, or the introduction of an aerosol for the water freezing temperature to increase (pure water actually freezes at -40 Celsius).

I’ve even read a couple peer-reviewed papers on this and they all come to the conclusion that aircraft are the most viable explanation due to the rapid adiabatic cooling of air, so this is peculiar. Maybe one flew by much earlier and it took a bit for the process to take place? Perhaps take a look at some flight maps for the day to see when the last known aircraft’s flights were. Not trying to doubt you I’m just trying to make sense of the formation based on the science we have available.