Since this isn't a scientific paper that presents data sufficient to support its conclusions, we can't judge it purely objectively. It presents itself as an engineering safety analysis. The first step in judging an engineering safety analysis is usually: was it performed by someone qualified to perform such an analysis? We typically want them to be performed by people who are both domain experts (in this case, nuclear engineers), and specifically people who are experts in assessing the risks in that domain, as well as in the general science of risk analysis. If a safety analysis is done by someone who isn't such an expert, it's quite rational to give it lower weight, because we aren't confident that they're familiar with all the relevant science and possible risks.
I mean, would you argue it's also a genetic fallacy that I take articles in Nature more seriously than I take articles in the Daily Mail? That I believe what Richard Feyman's lectures have to say about physics more than I believe what some random person on Geocities has to say? It just seems like good sense to me; considering the source of a claim is a good first step when deciding how much weight to give it. Bayesians would agree! It's possible that the Daily Mail will publish an insightful new analysis of global warming, but it's not very likely, and I would probably want to hear confirmation from a more reliable source before I believed it. Same here; this analysis is interesting, but I'd have more confidence in an analysis performed by someone who's actually an expert in the field, so until I hear one of them say that it's correct, I treat it with skepticism.