I couldn't find the specific rule on this but that makes sense.
The closest I found is: "› In the event that the winning bid is a false offer, the bid will be made void, and the auction win will be offered to the runner-up."
If it is considered null then the winner is indeed the runner-up Nodimbo with 1.6m.
I'll edit the post with the correct winner.
I've asked a mod for help on this, so I'm leaving the post open in case they confirm otherwise.