Yep, as long as the gambler haven't did anything wrong, why does the casino reserve the right to cancel the promotion? lol. That's like when gamblers won big amount on their casino, they become mad and didn't want to pay the winning, since they have a rule to cancel the promotion, he can confiscate the winning amount of the gamblers. Trusted casino wouldn't do that and Rocketpot already survived for many years.
They have a good intention to pay $16K few days ago, I don't smell they will scam @OP at the current situation so far.
I think that it is not so much to the Rocketpot.io to become a scam. Yet, as you said, they paid $16k, that means they are ready to pay. I`m sure that no one wants to pay some part of the big prize and after that become a scam - it`s better not to pay.
But the same time i think that they will pay with their rules - $10k per week and $20k per month. It may be useful to their money statistic not to show a big win in one month.