SFFP: I can only comment on my experiences. It never happened to me, but I've seen it. Perhaps that's the difference in Services. The RAF has annual GDT for all staff, and that's surely training. I would agree that a training deficiency would be more prevalent in folk who only go on the range once a year.
In the Army, it's a much more common thing to be on a rifle range, and only a few times in your career would it be under instruction (ie basic training, career courses). Turning round with a loaded weapon during a shoot is stupid and very dangerous. In my experience, such behaviour met with a swift corrective boot or fist. Nobody involved, either the range supervisor, or the firer, or anyone else on the range thought it at all unusual or wrong, nor did it ever go any further.
I don't suppose pushing out "knees to chest" in the Sgt Major's office while explaining why you had transgressed is in the relevant discipline publication either, but it makes short work of a disciplinary chat.
All been replaced with AGAI action now in the Army, so granted, things have moved on. I don't imagine the Pet Op involved will get away with an AGAI in this case though.