This is yet another fear based article while it carries merit to it the wording and general presence indicates that there is a vulnerability that can cause you to loose control of your vehicle. It wasn't triggered by the car driving next to you without first getting access to the vehicle physically, and it could possibly be exploited by a another vendors third party plugin.
Yet this is the same type of article that helps to fuel the auto industry in it's goal WRT the DMCA. They maintain that allowing anyone access to the ECU and the on-board networks of the vehicle creates a major security risk. This is all true but but this form of "MASS" presentation "Remotely cut the brakes!" helps to stifle the claims that the automakers are only trying to protect a future revenue stream. But gives them even more ammunition to lock odb-II and begin making it so you can access nothing in the vehicle.