Cas is a user on cybre.space. You can follow them or interact with them if you have an account anywhere in the fediverse.
Github issue of the moment, based on what bugs me the most... ;)
"Display followers-only toots from accounts you follow in hashtag search"
https://github.com/tootsuite/mastodon/issues/4701
If this bothers you too, head over there and click the thumbs-up 👍 at the bottom of the post. :)
