Only admins can do site bans. What you’re seeing is a hacky/temporary feature of the upcoming Lemmy v19.4, of which lemmy.ml is running the pre-release: when an admin bans someone from the site (temp or otherwise), it also automatically bans them from any community they have ever participated in. Lemmy.ml has always been the “beta” instance for new releases.
This is the most hyperbolic take yet 😂 I can no longer sit back and allow Communist infiltration, Communist indoctrination, Communist subversion and the international Communist conspiracy to sap and impurify all of our precious fediverse memes.
Edit to add: oic, your alts keep getting banned