Yeah the license wording is very unclear but in the docs he tries to clarify. From the docs:

    You must publish your work under the very same conditions. This means that other people could use and profit from your derived work.

    In any case, you are the sole proprietor of the books published with easybook, including all the copyright and related rights applicable in your country of residence. You are not obliged to share these works in any way, even if you benefit from them financially.