Mastodon does not store passwords in plain text. This is trivial to confirm as Mastodon is an open-source project. We use the bcrypt algorithm for one-way hashing of passwords. I can't believe someone is spreading misinformation about something so trivial to debunk.
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!