If its not automated how come there was a massive 1000 ish ban at once? each case has a different context, doubt you had the time to check it out with such a short amount of time with so many bans.
Posts are reported to moderators who check out the report. If the poster needs to be banned, the moderator sends a ban report up to a global mod or admin. The global mod or admin handles all of the ban reports they get at around the same time. Either the admins or global mods don't need to check every account because they trust the moderators to have already done so, or they check quickly because every such report contains references and links to the plagiarism post and to the source text so checking takes little time.