Objective C / C static method performance-Collection of common programming errors

Here is a method from a class in some of Apple’s example code. Why is this method defined as a static C method rather than an Objective C class method or a class method? In the context in which it is used I suppose it needs to be as performant as possible. Is this why? Is this the most performant way to declare a method?

static BOOL lineIntersectsRect(MKMapPoint p0, MKMapPoint p1, MKMapRect r)
{
    //Do stuff
    return MKMapRectIntersectsRect(r, r2);
}