In a Ponzi scheme you take new money fully aware that you aren't going to be able to repay in the medium/long term. In other words: you know you don't have a scheme that actually works well enough to pay the profits you are promising. This is not the case here at all. If the complaint is true - which may or may not be -this is theft, plain and simple.
Note that the difference between a Ponzi scheme and a recklessly run investment shop is sometimes academic. One can sometimes be unable to tell apart failed, unrealistic expectations and successful fraud. But here the business model is solid and they have simply taken from users pockets for fun and profit. Again, if the complaint is true.
Bit tired of hearing "Ponzi" misused time and again. I guess it makes for sensational headlines.