They do randomly select people from PreCheck and this looks like a fairly standard patdown procedure, which I have had to undergo countless times. (Much of my flying was/is through non-precheck airports.)
For the record, I'm not saying I support this absurd security theater, I'm simply stating that I don't think you got anything out of the ordinary. My favorite way to make them even more uncomfortable than they usually already are is to make soft moaning noises during the patdown. Definitely immature, but also worth it to see the discomfiture of especially aggressive agents.
Also, submit any extra complaint you can. Until these goons are relegated to the dustbin of history, it's worth raising every extra bit of fuss that we can.