Their thesis is that many of the home countries of H1B visa holders do not have the social, technological, and economic infrastructure to support lots of jobs with the skills that they are able to use to their potential in the US.

Thus, if they go home, they will not likely be "lifting their country out of poverty"—they will just be stuck in one of the jobs that is available there. Low-skill, low-pay jobs, without any prospect for advancing to something more like they would be able to do here.

I don't know to what extent this is true, but this is my understanding of their post.