Sensor to detect a basketball shot

Hi there, we're wondering if anyone might know what sensors this guy is using for his light up basketball hoop. Here is a YouTube video showing the install:

About the 1min mark you can see there is one small sensor attached to the net and another to the rim. Seems to detect both a shot and a miss/rebound pretty darn well.

My initial thought was an IR breakbeam but clearly this is not what is being used here.

Thanks for any input.

Accelerometer or piezo.