"Time is fluid." He answers almost immediately, though...he hadn't intended to make any move through time, and definitely not in order to watch himself.

The most ready explanation is that this has something to do with the TARDIS. Besides, when has someone who so eager to be called a friend ever been trustworthy? He keeps watch over the scene in front of them, but he's definitely on his guard now. He stands a little straighter and even feathers are more puffed out and demonstrative than they had been. He's waiting for the twist here, and he really doesn't like not being in control. "What would I need to defend myself from?"