https://medium.com/dark-mountain/fatal-flaw-with-mastodon-1ef0cb1965ed
He mentions that the system is distributed, but obviously hasn't grokked what that actually means.
Servers have user accounts. I know, shocking, isn't it? Same applies for email, xmpp, forums and just about any other service located on a server. They're not all magically synchronized by some universally agreed protocol. Nor would it be reasonable for them to be.
If you want a pre-internet analogy, there could be Bob living in Manchester and Bob living in Glasgow, and they might be different Bobs!
Scandalized? I thought you would be.