Definitely a mounted hand gunner there, and this was back when they were an iron tube on the end of a piece of wood. That is so cool to see.
In fact, in the lower left corner of that same picture, there appears to be a rider pointing with something. It could just be a bow or a wrapped bow, but it might also be a hand gun. Not that it is shown being fired from the horse, but again, it is none the less interesting.