Why are some social questions from Fluther listed at Sierra Club Green Home?

This social question from Fluther is also listed at Sierra Club Green Home.

I am aware of the beta testing and the federated category, but I thought that only involved questions from other sites coming here, not our questions going to them. If environment is listed in the tags of a Fluther question, will it automatically go to this other site? Is there a way to opt out of this?

Will I find my questions on other sites as well?