Well, I'd say, both controller and the pilot can do better. As for the pilot's side, he should be aware that he's in America where altimeter is used over QNH. (But! most CX pilots are British and Aussies, so.. tho most of those dispatched on US routes based in US )
About the controller, as mentioned, QNH is an ICAO language, so controllers so be aware with that. (not quite sure what FAA requires) Ofcourse she is not required to issue the converted pressure setting in hpa.
No offense, but QNH is rather common in the world, i guess it's the US and Japan still using altimeter, while Japan includes QNH setting in METAR.
Is QNH in millibars? or in Hpa (Hecto Pascal)?
They can be in either one.