If I’m last in a construction zone with a work stoppage (or very slow movement), I always put the 4-ways on. I’ve driven close to a million miles, mostly on interstate, and everything I’ve seen and learned says outside the flow of traffic do everything you can to make sure people who aren’t expecting a stop see you.
My drive is off a 45mph road (going speed closer to 60) and I always flash my brake lights several times to make sure they’ve noticed I’m slowing down.
As a defensive driver, I’ve avoided a lot of accidents (even pulling off the road for a big rig that couldn’t slow down in the snow), because I don’t want to lose my old car or my life!
I often do the same when it is obvious I am in such a zone - it sounds like the guy was surprised and hit the brakes hard...used to be when truckers were really up on situational awareness and safety but these days they act as if they are in sports cars....they are usually the fastest thing moving in foggy/rainy weather and I’ve almost been taken out by a few while going 30 in a downpour where even 30 was too fast....flashers and all.... one almost put me in the Genessee River when, the light turning green and me noting a truck over 1/8 mile away in the lane that just turned red (45 mph zone) - I turned right and looked in the mirror and he was on me...trying to run the light from over 2,000 feet away. I managed to hit the shoulder and hug the guard rail as he then stopped (in less than 200 feet) and he came back and asked what kind of fool I was because you couldn’t stop them rigs on a dime....I retorted that you also couldn’t speed them up and beat a light that had turned red while as far back as he was and he gave me a dirty look and returned to his rig....the original line that got me going was that some wanted to arbitrarily blame the drive of the car for causing the trucker’s demise and while it happens often enough, it also happens the other way around with at least the same frequency.