I don't know. But if you put your computer on sleep/standby/hibernate and lose power, it will have same thing too.

I don't think computer does anything in any kind of low-power state, including fast-startup shutdown. That would defeat the point of the low-power state. After all, if they need to do some critical task, they'll get it done before they turn off your computer.

Whatever the reason, the error doesn't mean damage was done, all it means is what it says: it unexpectedly lost power. Whether actual damage was done is a different story.

Also, apparently fast startup is not relevant for SSDs, according to some posts. I can definitely attest to the fact that you do not need fast startup for an NVMe boot drive.