Complicated.

Its a bit like people who make "fanart" of something and use the known brands and names as a way to get more attention sort of thing.

In this case its a little different as mastodon is more a synonym to federated social media especially to twitter like branches.

I´d say its not a legal thing at all but I understand him a little too. It also helps to know beforehand that a different kind of software is running.

Everything that is similar to mastodon should been given the rights to fair use the term "mastodon" as it helps to simplify things and not totally fragment everything.

I think he is from the same city I live in. :D