If you follow a Ghost site from Mastodon etc, it isn't just a one-way feed.
Ghost sites are actually on the Fediverse and they can interact with Mastodon etc accounts, they can favourite, boost and reply.
You can see Ghost site @sam replying to @FediFollows here: https://social.growyourown.services/@FediFollows/115293813549700275
This is two-directional, Fediverse-compatible websites can seamlessly talk with people on Fediverse-compatible social networks. This is how the open web is supposed to work.