Note how they simply said "because you broke this community's rules" without saying which. It's a type of kafkatrapping, a scummy but rather effective way to enforce hidden rules - if I don't tell you what you did, you can't prove that you didn't, so everybody else will assume that you did.
The admins in special really like this, with some ban messages being like "you broke the content policy" or "multiple, repeated violations of the content policy" (even after you did one thing). Perhaps not surprisingly some mods more "in-touch" with the admins do the same.
TL;DR: even if Reddit wasn't going down, see this as a blessing disguised as a curse. You've avoided shitty mods.