For the record, being quiet doesn't translate to poor interviews in this case. The MMI have fairly direct questions in a pretty tight time limit, as long as you answer the question you can do fine. Conversely, being loud and verbose can sometimes mean you try to add too much to your responses and interviewers cut you off before you make your point clear. It's a balance from my experience of bring on both sides of the table.
edit: my default position on people in med is to not believe anything they say about their own skills. If they say they're horrible at interviews, they're probably not. If they said they haven't studied much, they probably have. If they say that exam was the worst, it probably wasn't. And so on