Racism was a significant component of the drug war from the beginning. The article doesn't seek to "chalk it up to plain old racism", rather the article seeks to shed light on some of the racial aspects of policy making.
http://i.imgur.com/NkyayV0.jpg
The country was (more) racist back then, but we can't forget that the Black community was the first anti-drug community. Harsh drug laws were just how things were done back then.
Overall drug consumers have always trended white. Police resources are focused on sales, which happens in cities. Retail drug operations are designed around the laws, so the retail frontline people get swept up as users (because they carry small quantities), which impacts minority users harder.