Gregory's Server
That being said the nature of inaccuracy of that particular bot's data is doubly debateable. The number does align with what an alternative stats aggregator (fediverse.network) reports for Mastodon, however both include an infamous server that imported a large number of user records from its pre-Mastodon past. So while that server technically is running Mastodon software, the source of that number is different and should not be included in ours.
Then again you might argue statistics on anything fediverse-related will never be 100% accurate. Any stats aggregator relies on discovering servers to ask and those servers reporting truthful numbers back. There's always going to be deviations because one moment a server's here and the next moment it's having downtime. Then it's back again. With thousands of them. Of course some people have multiple accounts, and some accounts don't represent people.