You own the copyright to any works you create unless you have signed a document that specifically says you don't. It's not his responsibility to bring up the basic fundamentals of copyright law during a transaction, and there's nothing different and secret about them. If the messages constituted an implied contract, the only thing implied would be a license to use it in Minecraft, not a total transfer of all ownership. You may want to become familiar with said basics of copyright; Creative Commons has a good explainer https://certificates.creativecommons.org/cccertedu/chapter/2...