Data about a set of individuals can determine aggregate statistics.
Aggregate statistics can NOT determine data about an individual. They can be a heuristic, but not a safe one to blindly trust.
Lazy over-reliance on such heuristics is where racist/sexist/whateverist stereotypes come from: collectivizing a set of individuals by an easily identifiable feature, and then assuming qualities not determined by that feature to be true of the individual, instead of looking for actual evidence of those qualities.
It's a combination of:
collectivist mindset,
lazy search for easy answers,
trying to know more than you actually can by means of assuming,
and feeling good by confirming bias.