What does X% was found and flagged before anyone reported it mean? If they removed the content before anyone reported it, how do they know it was an actual viol

What does X% was found and flagged before anyone reported it mean? If they removed the content before anyone reported it, how do they know it was an actual violation? Does everything get passed through a human reviewer? Otherwise, are they doing something like “number of things flagged by system” / (“number of things flagged by system” + “number of things flagged by humans, not flagged by system”)? I’d like to assume they’re not doing something so egregious, in which they could trumpet 100% accurate classification by simply classifying all content as violations. More likely they have some statistical confidence from human validations of the false positive/false negative rate of their model, but without that breakdown the data they’re providing does not address concerns about Facebook’s systems being biased towards censorship and false positives. Anecdotally supported by a couple recent public incidents, and in conjunction with the lock-down of API functionality signals a turning point towards a new era of cautiousness and conservatism for Facebook...