As they said, racism is still an issue, but lack of role models and exposure is possibly a bigger issue. Lack of exposure and role models is a symptom of long term systemic racism though, but it doesn't manifest in the same way many people think of racism. Lack of positive thinking isn't quite the right term here, because it assumes that if Black kids just believed in themselves and thought differently it would fix all issues. It goes back to a stereotype that Black culture doesn't value STEM or intelligence, which isn't the case.