Key keyholing is when the bullet strikes the target sideways.
In my experience a light powder charge will not cause keyholing by itself. At the minimum, it would have to be a very slow twist with a long and heavy bullet, plus a light powder charge, and even then a true keyhole would be unlikely, if within a reasonable distance. It would likely result in just an oval shaped hole in the target. If the range is far enough though, it could result in keyholing.