@RGrunblatt Looks like one way for them to prevent that would be to switch on limited federation mode, which is quite the hammer and would block automatic federation with other servers https://docs.joinmastodon.org/admin/config/#limited_federation_mode
This doesn't sound practical for a news organization.
Another option would be to uncheck "Allow unauthenticated access to public timelines" in /admin/settings/discovery but that would kill the local timeline too.