The article discusses bike infrastructure in the context of cities. Population density of U.S. cities is comparable to those in the Netherlands. Some are much more dense, some are less. I'm unsure what point you're trying to make.

Parts of it do, and they don't see nearly the cycling mode-share as places in the Netherlands with equivalent density. The difference is infrastructure.

i guess you're trying to be snarky here, but, the density of the US as a whole has nothing to do with supporting urban cycling infrastructure. nobody here is talking about facilitating long-haul inter-urban bike routes.