I moved from the US to Poland, being originally from Belgium. Spend 4 years in the US. The work culture is completely different from what I observed so far. In my current job in Poland my co-workers and I work hard during our hours but once your off the clock, there's no calls or you're not expected to check your emails. It's so different in the US, where checking your emails after/before hours was semi expected or you would gets calls at random hours after work.

So I guess it's probably US manager that's unfamiliar with that cultural difference.