I personally will eat OUP on Pesach but it is very disturbing that someone would make fun of somebody who is machmir to use heimish hechsherim.
Your friend found a Domino OUP bag under the heimish bag, so what? The point is he doesn’t rely on OUP unless the heimish rav says to. It is money well spent.
It is a valid chumra and not to be scoffed at.
Those who scoff at it are “leitzim”, go read what chazal have to say about “leitzim”. (Those who scoff at those who don’t eat heimish are leitzim as well)