Not necessarily, but that is always true, even for, e.g., GPL-only projects. I.e. a GPL-only project might recieve a patch, but if the patched code does not contain a license covering that patch, the project does not have a licence to the patch and cannot use it. The usual way this is fixed is by having clear descriptions in your developer’s documentation on how to contribute patches and what licenses must be given to recipients in order for you, the software maintainers, to accept the patch into the project.
See further this post:
https://sfconservancy.org/blog/2014/jun/09/do-not-need-cla/