Site feeds Activities are publicly accessible unless the activity refers to content that the user does not have access to. If feed functionality is required for a restricted group of users, a site feed should be used. Site feeds display posts and replies among the users of the group. Site feed posts and replies display in the Newsfeed of a user only if the user has access to the site feed. Site feeds do not display system-generated activities. By default, the site feed feature on a team site is enabled. When you assign permissions to a team site that hosts a site feed, consider the following:
- Access to the site feed is restricted to the users specified in the
- Users can post or reply only if they have the appropriate
- Security trimming is enforced. This means that no site feed
activities will appear in the search results of a user who doesn't
have access to the team site.
- Site feed activities appear in a user's Newsfeed if the user has
access to the team site.
So, this clearly tells, if user dont have the permission to site, even follow the site, but will not get the site feed activity. SO make sure user does not have permission...You can check from
Site setting> site permission and check user permissions.