Yes, that was how I read it too. Sure, it's not a good thing to do. But Hermione's still relatively young, and under a lot of pressure (not just with the Ron thing - she's worried about Voledemort, and about Harry, and probably about exams too - and sooner or later, something's got to give) I don't think it was pre-meditated, either. She just snapped, but I don't think it was indicative of her 'normal' personality or behaviour