There are a great many old Ruger Single Six revolvers out there. They are great guns but like all older single actions, the hammer must rest on an empty chamber. A lot of shooters and owners of these revolvers don't know that.
Case in point, a very close friend of mine bought one of these revolvers used several years ago. He took his girl friend to the woods for a little plinking. He had the revolver in a low cut buscadero holster. They were crossing some rough terrain, the gun fell out of the holster, evidently the hammer struck a rock and the gun discharged. The girl was shot in the leg.
My friend felt so bad about it that he married the girl. She spent the next ten years making life miserable for my friend. He died of a heart attact at the tender age of 37. He was probably glad to go.
But my point is that he simply didn't know that his revolver needed to be carried with the hammer on an empty chamber. He had several guns, but he had no experience with the older SA's.
And I often run into fellows at the range with reproduction SA's and, of course, they usually haven't read the literature that came with the guns telling them to load five. I count their shots. If they shoot six times, I'll go over and chat with them and show them how to load their revolver (load one, skip one, load four, cock and let the hammer down). They invariably appreciate the information and the safety cautions.
So sure, if the fellow's gun fell out of his car or if he dropped it, it could have very easily discharged with a round under the hammer. And chances are that he had no idea that he had done anything unsafe...until his wife died.