"You're not wrong," the Doctor said, glancing knowingly at Bill. She'd made a comment about Sci-Fi when she first arrived, too. "The TARDIS is able to travel through both Time and Space... well... usually. Something's preventing her from doing that here, but I'm still trying to figure out how to override that." He wandered over to the console and began pushing buttons and flipping switches, then commented sarcastically, "You'd think that the people in charge here don't want us to leave."
This was his way of easing the conversation in a new direction.