john_henry is a user on octodon.social. You can follow them or interact with them if you have an account anywhere in the fediverse.
If you don't, you can sign up here.
From the faq: I don’t get the local vs. federated timeline thing.
“Local” toots are from the server you signed up at. “Federated” are the all the toots your server knows about. (It's complicated, but short version is: “toots from people that you and other locals follow.”)
hmm. interesting.
