Well, I suppose the argument would go that a Taiwanese engineer would, by dint of shared language and culture, be more susceptible to coercion and bribes than someone from europe, south asia, etc...

And I agree that you don't want to be too paranoid about this stuff. But at the same time, if you were expecting and looking for an "illicit backdoor" in hardware, this is exactly the kind of thing you'd expect. Firmware in a place virtually no one knows about gets modified on a per-product basis to do nefarious things. And this is exactly how you'd expect such a modification to be discovered, by accidentally introducing a bug that distinguishes itself from the clean parent.

I mean, I'm not screaming "spy" here, but if I were to have read this story in a techno-thriller novel I'd be writing a post applauding the author for her excellently researched and eminently plausible plot hook.