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Apparently, based from the comments, it was because he could clear his own trades

Clearly he couldn't. Not only that but the whole Nasdaq and other exchanges (mutual fund) struggled at doing that. Something is wrong.

Well, that's the point -- he couldn't. He was also trading from a personal account it seems. Seems a bit odd they would allow that.

The rules also allowed a single trader to own 25% of the marked[0].

Futures is not quite the same as 'owning' the market/asset...