Do you think it is safer to use Google Glass for texting and doing other stuff that you normally do on your smartphone, compared to using a smartphone, while driving? Anything that distracts you, is distracting. Even when you’re using earphones while talking on your phone while driving, you are being distracted. Although, according to a study mentioned in this link, people are more capable of controlling the vehicle while using Google Glass during emergencies compared to using their smart phones (because the hands are occupied and not on the steering), the wearable gadget is certainly a distraction.
The purpose of the study is not to discourage people from using Google Glass, it is more of an effort to find ways to deliver information to drivers with minimum risk.