My nephews are mistaken for being mine all the time just because I'm out somewhere with them, talking to them the way I would any other kid I was caring for family or not. My SISTER used to be mistaken for being adopted by ME when we were younger. I was still young looking myself, and people had a hard time believing a sister would take care of a younger sister the way I would... they assumed me a young mother (somehow) to an adopted mexican girl. (She isn't mexican.. she just tanned well, where as I got the same amount of sun and I did not tan at all.) And they thought I was a saint, somehow, for adopting outside of a 'white' child domain.
It is racist, and ridiculous. What you're saying is it is OKAY to assume things just because it isn't common? I mean... It is not common for a guy to like the color pink. Can I assume he's gay if he wears the color? I mean, that's okay, right? Where do you draw the line on assumptions? There were literally NONE other clues to indicate this dude was a criminal potentially assaulting/kidnapping this girl OTHER THAN HIS RACE AND GENERAL BIGOTRY. I wanted to highlight that, because it is important to note that you need BOTH for this to become a problem. His race alone is not an issue. It is the racism that creates the issue.