The problem with that assumption is that there will have to be 3 accounts with the same seeds to make sense of that theory. At the end Robinhood clearly showed the advantage he took of the flaw by winning many 10 BTC bets. So he probably didn't reveal the seed on that account, as he knew the rolls.
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Or perhaps he had 2 separate pairs. If he managed to get seeds off 3 accounts, then there definitely exists or existed a flaw. I wonder why Stunna still hasn't commented on it.
My guess would be that he had a way of making pairs of accounts with the same server seed. So Hufflepuff and Robbinhood had different seeds, but each had a 'twin' that was used to reveal their seed.
Of course, that's just a guess, and we'll have to wait for Stunna's edit to really know.