They have been doing this since last year, and Trustdice is still up. They managed to hold on to their reputation and still make a profit until now; I'm sure they will not offer that kind of return if they cannot sustain it. They are doing this to attract many players to play so they can claim their native token, TXT, and stake it.
It may look unrealistic, but not for a casino platform with a good standing in the gambling industry; I see it as a gesture of generosity to their community.
True, as I read the FAQ and the discussion, it seems the reward is dependent on the profit on a certain game (dice) and distributed to the stakers. I do think this kind of approach will be sustainable in the long run since it is based on the possible profit of dice.
The support staff probably gave a shortcut explanation which I think is somehow misleading and gives @OP confusion, the reason why this thread was created.
Sometimes those support agents are confused and can promise what is not, all you need to do is to take extra step to read through the terms of service on Trustdics because that is the only way you can determine what is uptainable in such a service or promotion, although the potential rewards of 2% is unbelievable but I know when you read through the terms and conditions you will understand all that it takes to achieve that potential rewards.
I also think that the one @OP had chatted with is confused since the information that the support agent told @OP is different from what is written on the FAQ. My initial reaction when I read their conversation was the casino can't sustain such reward but reading the faq and finding out that it was just a potential reward and not a fix reward as the agent stated changed my thought.