It’s hard to say, to be honest. Could be many reasons.
In my case, I was shy but did try to make an effort, but eventually stopped because, even when asking innocuous questions, I often got looked at like I’d just sprouted a second head - yet, I also heard other kids saying they thought I was stuck up, because I rarely spoke! Vicious circle. I did end up wanting to be left alone too, anyway.
The racist stuff may or may not be anything to do with how he was as a teenager. My dad was racist and had a faux superiority complex, but wasn’t shy at all.