Since you are a driving instructor you understand that ANY vehicle with properly operating brake system has more than enough capacity to lock up all wheels on dry pavement, or actuate ABS. Let me repeat, ANY modern vehicle.
Now the ABS, stability control, traction control, and a myriad of other "features" (ABS, SBS, SCBS, BFD and others) get between your foot and the brake pressure applied to the pads. I don't know about the CX5, but I know plenty of other cars modulate the brake pressure based on what they THINK you are trying to do. My E36 M3, while under heavy sustained braking, like T10A at Road Atlanta, coming down from 125 mph or so, will actually kick back at me, and move the brake pedal back towards me. And this is a relatively ancient car at 15 years old.
Since you have track experience, I suspect that this is what caused the problem, and it is possible that Brake Force Distribution (BFD) or some other "feature" saved you. Why would track experience create your problem? Because most experienced instructors have honed their skills over years of on track experience, to NOT activate ABS and to modulate the brake pedal accordingly. Unfortunately, with all of the safety features the pedal feel on many vehicles is impacted.
You are implying that you were unable to press the brake pedal hard enough to engage ABS and achieve maximum braking force, and the car intervened and added braking force. Others have said they think that SCBS won't activate with the brakes applied. I don't know. I only know that it can't miraculously increase braking force if you are applying adequate force to the pedal. It *might* increase braking force if you are not applying adequate force to lock the wheels and engage ABS..