Considering that their literal stated purpose is to create a curated list of 'nice, well-run servers', I don't see how delisting someone is remotely outside of their wheelhouse. If a server is federated with meta, it's not well-run. Easy peasy.
Nobody needs to be listed on Fedi Garden or has a right to be listed on Fedi Garden. They can still federate or defederate as they wish, just as Fedi Garden can choose to list them or not as they wish. Everybody gets to do what they want, as is the point.