Many auctions only have a single bidder, and in this case, the price is a 'reserve' price set by the publisher (website). That is common in ad slots which have strict targeting criteria banning nearly everyone else from being eligible.

In those cases, often the advertiser sets a super high bid, just to make sure they win the auction. Assuming the eligibility criteria keep all other bidders out, that's not an issue.

It looks like what happened here is the 'Yellow Ad' found a way to be eligible for far more auctions than normal, and had a very high bid. That meant it was now a 2nd bidder in lots of auctions where the price was normally set by the 'reserve' price, and the final hammer price was much higher.