I think it’s worth having the rules say “source available” or just “the source code must be published on GitHub” if that’s what you mean, because “open source” does imply an actual open source license to many programmers. Especially since right now the rules emphasize being open source and being hosted on GitHub as two separate things
Same thing for the rules about assets - there’s a big difference between assets that are “free and open source” and assets that are simply free to view/use. For me personally the former implies that e.g. art assets have to be Creative Commons licensed (or similar).