Thanks for using park.io and I'm glad you had a good experience.
park.io doesn't just get domains from drop-catching when they expire. Sometimes we buy them from the previous owner directly. Also, not all sales go through the drop-catching/auction process, for example users can park their domains on park.io and set a "Buy it Now" price for their parked domain, so domains also sell in this way.
file.io was never listed because it never expired/dropped or went to auction. We bought it directly from the previous owner and it was parked on park.io. I have now used it for the service posted here. What you quoted above was said to advertise park.io, and I apologize if it is misleading.