You are confusing the "individual mandate" with the "Affordable Health Care Act". Perhaps that explains why this keeps getting reported incorrectly. The Act itself was declared Constitutional as a tax. That was the whole controversy with Roberts - that he literally re-wrote the bill to make it work by calling the "mandate" a tax.
While Ginsberg voted with the majority, she wanted the mandate to be declared Constitutional which Roberts disagreed with, and that is why she wrote a separate opinion.
So while the entire Act was declared Constitutional, the individual mandate was not. That is the inaccuracy - might seem subtle but it really isn't.