This is how money works.... i have the same problem with my github projects but i dont realy give a fuck on it.
#Edit
the github project is also linked in his thread
so if its modified and not only c&p therefore there is no worry
i think its acceptable
the github project has MIT License
so the owner of the api is allowing modifying and selling the project
All infos can be found here on his github account: https://github.com/Michidu/ARK-Server-API/blob/master/LICENSE.TXT