^It is a bit strange. I think what probably happened is that, when asked that kind of question, Sam has a standard response that she gives about believing that she can win.
She was just saying the first thing that naturally came to mind.
It is interesting that she chose to cover up the ankle surgery though. I'm not sure what the reasoning there would have been. Maybe she just didn't want the extra media attention ...
I'm pretty sure this is what happened. I also suspect that she was put on the spot about her injury by some journalist who somehow got wind of it.
I find it hard to believe that she would keep it under wraps for a month (remember all those pics of her happily training in December, as if she didn't have a care in the world?), and then suddenly, a day before the Aussie season starts, blurt out in a presser "My ankle is injured".