The article is discussing, at length, the author's view what constitutes the "blue tribe's" outgroup. Poor people of colour wouldn't, pretty much by his definition. be part of that outgroup.

> This seems to highlight Scott's small social circle if all the members of the "non-Red Tribe" are white yuppie coastal elites.

This is an uncharitable reading of text. I mean, you may be correct, but it isn't supported by the goal of the essay.