We’ve used customised accounts to create the communities, and automated accounts to boost them around the Fediverse so everyone can be a part of it. Unfortunately, notifications are a side effect which we can’t turn off due to the limits of Mastodon’s capability. The good news is that you can turn them off yourself. If you don’t want to follow a feed, and would like to stop seeing notifications: just mute the relevant Feed account. You’ll find them all at newsmast.community.