I didn't read too much into his use of "descendants", trying to be charitable in my interpretation. But having read his response to you I'm starting to have second thoughts...

Culture matters, and survives migration.

Now you're losing me. In what way does "culture" matter? Socioeconomic status has nothing to do with "culture".

Well as Devil’s advocate, look at how people in Japan reacted after Fukushima. The world was awed by how awesome their “community spirit” was - nobody denied they exhibited far more social cohesion, sacrifice and civic responsibility than would ever be on display in the US.

That’s a cultural difference on display. Culture is not determined by race, so let’s not conflate the two. Culture is something you are immersed in and it does influence behavior.

There are also massive downsides to extreme cultural cohesion, looking at it another way.

But let’s not deny that social culture has a bearing on individual and group behavior. It has a massive impact. Conflating that observation with race or _racism_ seems a particularly unhelpful neuroticism of the US.

I agree with most of what you say. It's just that culture in the US isn't nearly as homogeneous as culture in Japan, and I have my doubts now as to whether the poster in question was talking about US as a whole or the culture (read race) of a specific demographic. Also, your examples here entirely sidestep the subject, which is crime and recidivism, things that are also found in Japan, probably lower than in the US but probably still higher than in Norway.