Simple as that. This makes for legal complications if somebody wants to reuse the source; yes, the source is available, but no, you do not have the right to reuse it. My suggestion is to license the source code as open-source and the assets as all rights reserved (proprietary) or Creative Commons (reusable).

What is the goal of this github issue, the mod is licensed as All Rights Reserved, don't think anything different is needed.

I figured it might've been an oversight, seeing as the source is available but not reusable. If that's what you're aiming for, though, go ahead.

What is the goal of this github issue, the mod is licensed as All Rights Reserved, don't think anything different is needed.

what is a pirate's favourite license

If someone wants to use some of my code they need to ask, that's pretty much it from what I read. I try to make everything that could be useful to others end up in the library mod for malum; which anyone can implement in their own project.