Yea that's kinda odd, but the good thing is you already have an acceptance in hand. Maybe you could try some mock interviews?
Interview skills do matter, and there is a myriad of things that you can screw up on. I interviewed pretty poorly last year and I had no clue why, 'cause I have no problem socializing or holding conversations and I don't get nervous or anything either. Turns out it was my posture and general attitude(i.e. unprofessional and lackadaisical), which my friends helped me improve. You could ask some of your friends to help as well. It doesn't necessarily have to be someone who knows medicine, just someone who knows proper interview etiquette. Maybe ksmi can help if she has time?