It's a mistake to assume that this was not peer reviewed. The PNAS has two tracks, stringent peer review and direct submission from members of the National Academy of Sciences. Every article is labelled as to whether it was reviewed or not, and the vast majority of PNAS articles I see are peer reviewed. Those articles that go through peer-review are typically of extremely high quality and impact; it takes a very strong paper to make it through peer review at PNAS, typically.
