I'd just like to interject for a moment. What you're referring to as Mastodon, is, in fact, the Fediverse, or as I've recently taken to calling it, the ActivityPub Fediverse. Mastodon is not a social network unto itself, but rather another free server implementation of a fully functioning social networking protocol, working alongside many others creating a fully-fledged social networking network.
Many users on the Fediverse are communicating either with ActivityPub or OStatus every day, without realizing it.Through a peculiar turn of events, many users are attributing the merits of the idea of 'decentralized social network' to Mastodon, not aware that it is basically the same as all previous federated social networks with a nice frontend slapped on top of it.
There really is a Mastodon, and these people are using it, but it is just a part of the Fediverse they take part in. Mastodon is an implementation: a software that implements the standards as stated in the various specifications. Implementations are the most vital part of a protocol, but useless by themselves alone; they can only function if they are interoperable with other implementations of the specification, thus creating an interconnected network. Mastodon is normally used to access the Fediverse: the whole system is basically an ever-expanding universe of federated social networks software, hence Fediverse. All the so-called "Mastodon" instances are really just instances in the Fediverse.
Many users do not understand the difference between the implementation, which is Mastodon, and the whole system, which they also call "Mastodon". The ambiguous use of the name doesn't help people understand. These users often think that Eugen Rochko developed the whole system in 2016, with a bit of help.
Programmers generally know that Mastodon is just an implementation. But since they have heard the whole system called "Linux" as well, they often envisage a history that would justify naming the whole Fediverse after the implementation. For example, many believe that once Eugen Rochko finished writing Mastodon, the implementation, its users started to create more federated social networking software that was interoperable with it, and thus the protocol was alive and well.
Which is actually not entirely incorrect - the ActivityPub specification was already complete, but was struggling to find projects which could adopt it. However, it's important to remember that Mastodon previously worked through the OStatus set of protocols, which had been developed throughout the years and implemented by many different projects, including, but not limited to, GNU/Social, Diaspora, postActiv, Pleroma. Only in 2016 did Mastodon become a part of this network, whose creation is definitely not due to Eugen Rochko.