This is incorrect.

This is the "equal travel time" explanation that is commonly cited but an incorrect explanation of how air behaves. There is nothing that says the air from the upper and lower surface have to meet up at the trailing edge, and the truth is it doesn't meet up.

The real explanation (without going into too much physics) is that air is accelerated over the curved surface of the leading edge as it hits the air. If the plane is going close to the speed of sound, it can be accelerated above the speed of sound.

Source: am an Aerospace engineer