No, there is zero truth in it. It would be trivial to detect phoning home.

On top of that, all claims of this are written on devices built on Chinese hardware. That makes it a joke to worry about hidden backdoors in Chinese models. Completely inane to pretend that Chinese model backdoors (for which there doesn't exist a sliver of evidence) would change anything when near every device in the US contains Chinese-written firmware in some shape or form.

It's All-American FUD.