Not sure. I've never had anyone complain of groin popping. Hips or knees may pop. Ligaments or tendons may pop or snap. Let me tell you that popping/snapping is not a specific symptom that indicates where the problem is or what it is. It is audible and definitely draws attention, but in the absence of other symptoms, namely pain, limitation in the range of motion, it may be nothing to worry about.
I've had that. While I can't be specific, it is a ligament or tendon stretching. It's not harmful. If it hurts, you should get it checked out.