Post needs to have the title updated. Even though it is called OpenMower it is not open source, it uses the CC-BY-NC-SA license. The readme of the project has been updated to remove the claim that it is.

Of course a person is allowed to license their software however they like. However, I might also note that creative commons is not recommended as a license for code: https://creativecommons.org/faq/#can-i-apply-a-creative-comm....