It mentions limited functionality if you don’t pass it an account so likely as not it’s passing your user token along with a web browser header, scraping reddit, then yanking out whatever it’s filtering and then serving what’s left (likely just the text and vote metadata) in a locally hosted or remote hosted (not on reddit servers) site.
So it wears a mask that has your usernames face on it, knocks on reddit’s door, asks reddit your question, then comes back to you with only the relevant info that you have told it to bring back.
That’s only if my cursory reading is correct. I’d defer to a dev or someone else more interested in the project.
Well Torvalds was only one guy for the first couple years.