The more I sit with this the more this seems like a rationalization. Being a good contributor is a human quality, not a quality of the tools that you use. Are you thoughtful? Do you place the needs of the project above your own? Are you easy to work with. None of these things have anything to do with the tools you use. Perhaps they have a bias where they think that LLM use indicates poor character? Good luck to the project. We will see where this lead them.