We must remember a lot of people use these forums to learn experience and develop their skills. It's important to stress the lessons about making valid reject decisions. I have had selcal go off on takeoff roll- it was just an eyebrow raising event with no thought to reject. Via HF, you are not going to receive any information in those seconds that is of any importance, and students must understand that a reject is a fairly serious event, even at low speed, and such a decision must be taken sensibly. A reject creates a hazard and stoppage on the runway requiring extensive ATC intervention, and some airports require an automatic runway inspection as they don't understand what has caused it.
Selcal alerts are not unusual, even when apparently nobody is calling you. Maybe it is a slip of a radio operators hand, or just spurious warnings. Perhaps we should have it disabled automatically when the wheels are down and not compressed.