When is the last time you saw someone purchase illegal drugs online with dollars?
I'm not sure that it matters whether it is online or face-to-face. The article didn't qualify the spending as being online but rather a broader statement that encompassed all spending.
Also, I'd like to point out that there are many, many forums where people can buy pharmaceuticals from guys in other countries, and much of their exchange is done via PayPal or Western Union or MoneyPak or whatever.