Why happen if I store pirated content inside my VPS? I think the answer is pretty obvious, in their TOS should say that if I do that they will BAN me without warning, but can they detect the files? Or worse, what if I download directly into the VPS with torrent or Jdownloader?
From what I understand (and based on USA laws) only if I torrent something they can BAN me, because I'm redistributing something with copyright in their servers, and I don't only refer to games, this can apply to music, movies, etc.
Given that the Fediverse is wide open, unencrypted, and your instance owner is no more immune to getting a subpoena from law enforcement than anyone else ... one might think twice about asking questions of the form "if I commit a crime can they find me" here. Even if your VPS can't detect it, you just left a paper trail here by asking how to commit a crime. :) Bad plan.
Your Fediverse instance owner might consider deleting your post and perhaps your account to keep them from being the subject of such a subpoena in the future.
Not just your instance. Every instance Federated with it that got a copy of your post is part of the chain of evidence. Don't plan crimes in the fediverse for heaven sakes.