Modern ECU's are quite smart: a lot of computational power is in all of them. There are a few different systems in place to detect knock and any events should be logged and stored so that you have a trail when pulling info off of the ECU.
If the techs pull this info and find little to know knock events in the counters, or if clear them and run the car (could attach to OBD and see any events in real time), this would likely show that no pre-ignition events are occurring. That's a good thing.
Knock can be pretty hard to hear at RPM: lots and lots of noise going on. This is why you must rely on sensor output to see how things are going under the proverbial hood.
I spent a lot of time looking at log outputs with my old car and its very primitive aftermarket ECU, and knock curves stood out like a sore thumb. I ran a winter map to compensate (thank you crappy blends on the east coast). I should not complain I suppose since West Coast gets cat piss for fuel. Their 91 octane...ick. AZ/CA/CO all those states are fuel challenged for high performance.
- b