My personal impression is that people use an email not easily traced to their identity, if they are concerned about that.
You should also be aware, even more than on commercial social media, that what you say and post is essentially public property. Due to the nature of federation it is rather difficult to track down and remove all instances of your content from any and all servers it was federated to, if you wanted to do so.
I think that guy is trolling. Or has severe brain damage