Okay I really appreciate the feedback and different perspectives.
I've already reduced my worry to near zero, in part b/c experts here have convinced me this could easily stay a one-time occurrence, but also b/c 10x more milage has seen no recurring event. This happen with the odometer at < 20 km. But people might benefit from a bit more detail:
First, I actually like the idle/stop feature and have known about it for years. Watching my {uber, grab, bolt} drivers I noticed the behavior and ask if the vehicles were hybrid (because I noticed a similar thing on Priuses, the Toyota hybrid). Nope, petrol only, so I looked it up and thought "good idea". Fuel efficient.
The stalling event happened during a sudden and forceful stop, going down hill on a gravel surface. As I pulled out of a parking lot onto a main road, the lane was clear until, at the last minute, it wasn't. (A car passing on the left at high speed entered the leftmost lane where I was heading.) Due to the forward and downward momentum against the gravel surface, the wheels locked and the car stalled with engine light. Full restart necessary.
Now while the suddeness of the stop was at most a 1-sigma everyday stop, I suspect the combination of everything else produced a 2 or 3-sigma back "pressure". I'm spitballing here but there's a torque equivalent of impact force, which would be very high under these conditions, right?
I now consider it highly plausible the engine was designed to stall under such conditions. (A bit like fighting with the emergency brake, I'd want the car to stall, I think.)
Anyway thanks all!
Mods: please move to "cars for sale" ????