Crazy. I recently sold a condo to Opendoor for significantly more than I would have even thought to list it for. When I negotiated with Opendoor after their initial offer, I pointed out a recently sold condo (days before, in similar condition, layout and finishes) in the same complex that sold for much higher than Opendoor offered. Within hours Opendoor came back matching that same selling price. The kicker? It was a unit that Zillow bought.
The algorithms are fooling themselves... Opendoor matches Zillow who matches Opendoor and that's how you get ever increasing offers.
Edit: oh, and now Zillow has that unit on the market, priced 14% lower than they paid for it, after 3 price cuts so far.
Edit 2: Phoenix/Scottsdale AZ market