That's what centralization is. There's a central authority in a platform and it has the power to do whatever it wants to users. But, before doing that, there's a set of rules that they've made as a standard to be followed. So basically if an account is reported, you'll have that notice and verdict. Other than that, they'll detect if you've been doing malicious things like sending unsolicited links to others' inboxes. And on your case, you have the idea already, are you sure that you haven't done anything within that day after opening your account?
Facebook has rules that every account must obey. Disobeying any of these rules will attract some level of sanctions. If the platform observes that an account is fraudulent, it will be placed under investigation and a ban can proceed if evidence shows that the account has the intention or is used for crime. In some cases these allegations are untrue but the account owner has the right to ask for a review. Nevertheless, the platform is centralized, an account can be banned for other reasons such as ideological, religious, or political orientations. In recent times some politicians have accused some social media companies of censorship.
