Can confirm that pec popping is learned. I say this goes for a lot of muscles, the butt as well. Start training the chest, butt, or whatever and at first people will talk about activation, but you won’t know how. Eventually, if you continue to train, you’ll be able to really activate those muscles during the movements in a workout, and can flex them whenever you want after that.

I can do the pec popping, but I never aspired to do that. What really stood out for me was the butt. When starting to work out I’d always hear trainers say to use your butt to rise up out of a squat or whatever. I had no idea how to do this and no matter how much mental energy I put into it, I couldn’t do it. Then after doing enough repetitions it came to me. I can flex my butt to make standing up from a squat easier, and now that I know how I can do it whenever (not that I have much of a reason to).

It’s all about developing those neural pathways and that mind/body connection.