WIRED 3 days ago reported on it in a less confusing manner. Also it included a comment from Google

In a statement, Google said, “AG Paxton’s latest allegation—that we generated a ‘third price auction’ or manipulated our ad exchange—is entirely inaccurate. As of September 2019, we have been running a first price auction, but at the time to which AG Paxton is referring, AdX absolutely was a second price auction.”