It's probably just encrypted, that provides the security-focused part of write protection, at least while it's not been unlocked for boot.
Computers used to have stuff in ROM, stuff used to be a lot smaller, you used to be able to burn your own ROMs and put them on your own boards and have it be meaningful. But none of that is true today of course any more than that you could put a useful amount of storage on a floppy.
Read/write protection on flash is mostly done in firmware and therefore could theoretically be bypassed, I wonder if there were floppy drives before LS120 where that was also true.