I don't know where you get the impression there's no phantom braking in other OEMs. It's easy to find examples (they just don't typically call it "phantom braking" as that seems to be a term used mainly by Tesla forum goers):
Sudden deceleration while in Cruise Control - AudiWorld Forums
Adaptive Cruise Malfunctions - Scary - Ford F150 Forum - Community of Ford Truck Fans
Adaptive cruise control and random braking 2021 Q5e Prestige - AudiWorld Forums
Honda Sensing - Which Part Slammed On My Brakes ?
There's even a bunch of reported issues of phantom braking with AEB, which applies even harder braking, so is more dangerous (Tesla didn't seem to have similar cases of phantom AEB activation, just complaints in terms of AP).
Nissan's AEB is Suddenly Stopping Vehicles For No Reason
Audi, VW Automatic Brake Problems Could Prompt Lawsuit
Mazda3 Recalled for Sudden, Unexpected Emergency Braking
Radar is easily fooled by overpasses, large trucks, metal guardrails on the side of the road (very common causes of phantom braking). I remember overpasses/signs being the common trigger for Tesla's radar back then and they had to implement a whitelist system.
"Initially, the vehicle fleet will take no action except to note the position of road signs, bridges and other stationary objects, mapping the world according to radar. The car computer will then silently compare when it would have braked to the driver action and upload that to the Tesla database. If several cars drive safely past a given radar object, whether Autopilot is turned on or off, then that object is added to the geocoded whitelist."
Upgrading Autopilot: Seeing the World in Radar