It has happened to me twice, both GM vehicles.
BTW, I still drive GM vehicles.
In both instances, I turned off the ignition switch and was able to come to a safe stop.
The first time, I was 16 years old and experience wasn't a big factor. Common sense was. Engine running fast, car going fast, shut off engine. car no longer goes fast. Not too tough, even for a 16 year old.
I have to think panic is a big factor as well as people not understanding how a car works. The 911 operator must not have suggested turning off the ignition in the case that seems to get the most publicity. That was probably due to not knowing about cars rather than panic.
I think most of us on these forums are fairly car savvy, but there's probably quite a few that have no knowledge or interest in how things work.