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.
You buying it before posting it is no better than you drop-catching it.
In their FAQ, park.io writes that one of the reasons an expiring name might not be listed is "because we intend to order this domain for our own portfolio. We don't do this often, but every once in a while there is a domain we want for our own collection and so we do not list it on park.io."
A little disingenuous since the domain was never listed on park.io and this site was made by the same company as park.io.
Makes me believe that they snatch up the best domains for themselves so people can't bid on them.
I've bought multiple domains from park.io before and had a good experience, but I was always worried about this.