Lucky or Good?

It looks like the factory stud with just a little bit of pulled thread on the end. My thinking is that somewhere, there is an exhaust manifold that has a little over a half inch of the threaded end stuck in it. Other than that, though, very good job! If you want to do that every time you drill and its broken off flush, use a Dremel tool or the like with a small grinding point in it and use it grind a divot in the center of the bolt. You may have to start on a slight angle until you get some material removed and upright it slowly while applying slight down pressure.