True enough, but I would say that he ignores the earlier influx of the '48ers and the acceptance of Marx's rantings by some among a generation of northeasterners. Marx was a European visitor, so he's right about communism never being a homegrown phenomenon here.
Communism found its most fertile soil in societies ruled by royalty. The royals had been invited by Americans to keep their rule to themselves and Americans had created for their descendants an example which showed communism for the folly it is long before the Europeans who believed Marx's lies immigrated here in large numbers in the period he mentions.
I think he makes some good points.
Americans weren't much into unions or Socialism until after the late 1800s and large waves of immigration brought in the type of people to support all that. Before then there weren't the kind of people who would support Socialist programs in the US.