so I haven’t read about code that controls this - but my guess is that your device did have enough storage for the OTA zip and the unpack → but had insufficient space at first boot when creating the dalvik cache, as this one is with the userdata partition on the FP3.
The update mechanism would need to calculate some extra space for the dalvik-cache before update. Depending on amount of apps installed the size requirements can be different.
The teamwin recovery (twrp) has menu options to clear that directory. Could be implemented with the lineage/e-recovery menu too for users that have locked devices.
Why dalvik cache? after an update all dex classes of apps and system are regenerated. That’s bytecode optimization for the java apps running in the android jvm (aka dalvik).
Edit: and nice that Android shows the file-group for encrypted files, makes it easier to pick them out. It cannot infer the filetype at that point, but file ownership gives it away interestingly