At younger than 5 my child knew that, as apparently did you and yours. Neither of us know if this particular child didn't and it may just be that he did.
This debate is about whether a parent is responsible for their childs safety in a public place. That's the bottom line.
Of course that is the bottom line........but you are not giving the woman the benefit of the doubt here, even based upon your own anecdotal stories.
The bottom line really comes down to : WE DON'T KNOW.
In the article, Mom is quoted as saying she heard a crash. She didn't say she saw it. I can't imagine how she felt. Maybe I was different but I was very careful with my kids. You don't get a 2nd chance. Poor Darkchylde is 21 and I still try to grab her hand. Force of habit. lol You should hear the 35 yr old and 31 yr old when I try to do that to them. They look at me and say "Mom?"