If any code you've written (or anything you've produced that constitutes IP) is in their released product, they have to compensate you for it. In startups, the compensation is typically in the form of equity.
As others already alluded, in any case, it does not seem that you want to go forward in business with either the founders or the incubator.
As others already alluded, in any case, it does not seem that you want to go forward in business with either the founders or the incubator.