It's a valid assumption. Either you or someone else intentionally removed the insulator, or went ahead with installing the backplate without an insulator. There really aren't any other options.
Are you just here for an argument, or are you hoping I'll back down to make you feel better about doing something as silly as that?
Yet another (wrong) assumption
The purpose of the thread to try to assist the poor guy with his computer problem with advice or experience -which is what every contributor had done except you.
"Asking questions nobody can answer will not help you..."
"That'd be your fault for removing the protective plastic layer on the backplate."
Hardly positive or helpul to him.
"I am most certainly not an amateur. I have never seen a metal backplate without a protective layer."