It would not make sense to buy those coins at a 30% higher price and dump them at the normal price in the market. I am sure people who invest 13 million USD in the auction, and smart enough not to dump it right away
Common sense would tell that if the winner of the auction is paying higher than the market price, I don't think the guy will just dump it straight away to the open market. Somehow I have doubts whether the 30% claim is true in the first place. I mean with the money he has, he can opt to buy from different exchangers or even buy it in batches. What I think is that more likely the bidder might have won the auction paying at lower than market price.
You may be right about that. However the buyer at an auction is a different kind of buyer that uses the exchanges. (This is my theory). Exchanges are far to risky for an institutional buyer to use. They want to get $100K in one shot with no risk of fraud. A marshal auction is a very safe place to buy and that is worth a lot to a real investor. The big fish I know set up a private arrangement with a miner or look for a chance like an auction. They would not even consider sending money to an exchange.