Seems reasonable. I'm sure direct injection has something to do with it.I tought this was the big “breakthrough” with this turbo engine. The fact that it didn’t need higher octane to produce the same high torque at low RPM.
You are right with regards to detonation, but i think there are too many factors in play between different engines to apply a one rule fits all principle to knocking. Knocking is ultimately based on heat, and these engines have a lot of heat management solutions in place to attempt to prevent it (exhaust scavenging, cooled EGR, etc). It is possible that these solutions allow the engine to run at peak torque without having to rely on high octane fuel, but that they aren’t as effective at high RPM. This is all speculation on my behalf of course, but that’s how I see it unless we can get an actual Mazda engineer to dig into the details for us.
good info here if you are interested, although very similar to the youtube video above.https://www.wardsauto.com/engines/mazda-s-innovative-4-cyl-engine-pulls-big-v-6