Why do people think that being antisocial is you being shy?

A lot of people think I’m shy just because I don’t talk to them, but the thing is that I just don’t want to speak to them because I either don’t care to know much about them, or they do something that I don’t want to get to know them more. It’s so stupid, but girls especially think this about me. Even though I have no trouble talking to people.
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I don’t like most people, so I don’t go up to them like others. And I don’t fake a greeting, I’m genuine.
Why do people think that being antisocial is you being shy?
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