Why was there a round in the chamber when there's no safety?
Common. It is how they are carried.
I have limited experience with guns, but this seems really, really stupid.
I read about this article yesterday. In that version the woman was hugging him from behind on her knees... Also, there's speculation that the gun had after-market modifications to the trigger (but this isn't confirmed).
Carrying with a round in the chamber (called condition one) is common practice and there actually are safeties present, they just aren't external.
All cops carry condition one and many citizens do also who carry an a regular basis.
The reason for this is that it's really hard to rack the slide of your gun when there's a full magazine in it. It's not like the movies where they do the two-finger rack. Also, your average self-defense (for citizens not cops) shooting takes place at 3 feet, so you don't have time to be operating the slide even if it was easy.
Guns are being built with internal safeties like the firing pin block. The S&Ws have it (most have it these days). The firing pin block is a piece of metal that stands in-between the firing pin and the chambered round. When the trigger is pulled it gets pushed out of the way of the firing pin's channel.
So, if the firing pin (starting in the cocked position) somehow fails (maybe the gun is dropped or the gun is faulty) the firing pin will hit the firing pin block and not go off. These guns don't fire unless the trigger is pulled.