Reactive elements make stable compounds. e.g. sodium + chlorine -> sodium chloride.
There is no FL in periodic table. And Teflon is not as stable as believed.
He said 'F', not 'FL'. It is on the periodic table: https://en.wikipedia.org/wiki/Fluorine
Florine is remarkably not inert.
Teflon is a relatively stable Florine compound.
But as you say, it can destabilize when the pan is used within a few sigma of ideal cooking temperature.