Simply put, no one is out here to give you free money.
Use your common sense and you'll find that this is a completely unsustainable business model, and they clearly cannot afford to give away funds like this even if they are just starting out and what to advertise themselves. What if people abuse this promo and have multiple accounts? Wouldn't they go bankrupt overnight?
The only logical explanation is that they are running a con, based on the fact that they will most likely ask you to deposit more funds in order to withdraw any winnings from the promo code, or just not process any withdrawals altogether. Couple that with the fact that they're using the script of another site as anon mentioned, you've got an obvious one.