In charity we must assume that the episcopal residence was utilized for other purposes during his tenure.
Lord grant me charity though.
I know what you mean and second your prayer for myself. I am trying not to be uncharitable either to our Holy Father or to any others serving Holy Mother Church in their small ways. But, I do find myself wondering about these things and what they mean. Perhaps his house was utilised very efficiently and served the Church in some way while he didn't live there. Maybe he even used it as a shelter for people or some such (though surely that would be printed in every source if true) or just an office. I don't know, and won't pretend to. But, I do worry about people who are so persistently and publicly humble. There are people in this world who take a bit too much pride in being humble, and so I am not going to swallow down the media theme of our humble pope any quicker than I did their insistence that our last one was a Nazi. I will wait and see what some of the real fruits of his pontificate are and then decide what I think is true.
I believe it was used to house an order that had nowhere else to go.