"Vitamin K" is a street name for the drug ketamine, yes. But, there is an actual vitamin K as well.
Basically, a molecule gets classified as a vitamin if the body needs it to perform certain chemical reactions but can't make it in large enough quantities to keep up with the body's demand.
I'm pretty sure you can get your needed amounts of vitamin K from a regular diet (according to the wikipedia article), so I don't think there's much need to worry about getting an extra helping of it from rooibos. I'm not a doctor though, so don't hold that against me if I'm wrong.