I think the point is: "you'd be a fool not to prefer gas, because while the greenhouse emissions are about the same, for everything else coal is much worse"

They said gas over coal. If you accept the claim that GHG emissions from gas and coal are roughly equal, their claim is the other pollutants from burning coal make gas far more preferable.

If their greenhouse emissions are even close only a moron would not pick gas over coal because the former's emissions lack all the other nasty byproducts that are present in the latter's emissions.