I guess you must be a low-level developer then, because to application developer it would seem that sqlite write speed is actually bound by the file system performance (which it depends on).
The title is a joke, right? It's not actually "faster than the filesystem" unless it's not using the filesystem; it's faster than something else that also uses the filesystem because they use different system calls (context switching).
you can be faster than the filesystem, while using the filesystem, if you emulate something the filesystem does poorly in a more performant way.
That's what's happening here. storing files in SQLite removes any per-file overhead in the filesystem. The filesystem now only has one file to deal with, instead of however many are stored inside the SQLite database.
This is a very real phenomenon, and definitely not a joke.