He doesn’t usually do this sort of thing. In all of his randomness, one thing usually stays the same: he goes where the TARDIS takes him. Even when that’s not where he means to go. He goes where she takes him and the adventures, more often than not, find him. Every now and then, he’ll come when he’s called. But it has to be major. As in the-world-is-going-to-end-if-you-don’t-get-here-right-now-Doctor types of events.
This is most definitely not one of those events. Yet here he is, poking around a closed-for-Easter shop with Donna just because Wilfred is convinced that the shopgirl is an alien.
He’s right, of course. Wilfred Mott has a uncanny knack for stumbling into trouble. But that’s beside the point.