They’re correct that this creates cognitive dissonance. The racist, upon meeting a minority member that doesn’t uphold the stereotype, has two contradictory facts in their head:

1. All members of a minority group are bad.

2. This member of that minority group isn’t bad.

This is cognitive dissonance. Both of these cannot be true at the same time. One of these premises must be wrong.

Hollywood imagines the bigot will treat this like a physicist disproving a theory by finding a counterexample. But bigotry is anyhing but scientific. You can’t reason your way out of a place reason did not lead you to. Instead, they adjust their premises to:

1. Most members of a minority group are bad.

2. This member of that minority group is one of the few good ones.