I reckon it's instinct. Closest I ever came to this situation was when I was travelling along a two lane one way road. This person ahead and in the lane next to me assumed that it was a two way road though and tried to turn into a another street from the left lane (left lane drive) right in front of me as I was going 70km/h. My only thought at that time was to avoid em at all costs cause it would've been a rough crash given how big my van was compared to their car, I swerved in front of em and avoided a crash by mere centimetres.

So my instinct was to avoid the crash, her instinct was to scream which if confronted with a terrifying situation say 10,000 years ago would've been the right call, it just wasn't in this case.