Well, I'm a Catholic and I got a 1st in my Law degree and averaged 81% on my most recent postgrad course taught at Masters level. So I'm calling bullshit on this one.
On a more serious note, the review does undermine its own conclusion by basically saying "we need to do more research on this" - there's a lot of caveats in there, and as with any claim regarding "X group of people less intelligent than Y" I'm taking it with a sizeable pinch of salt. Not least because, with all due respect to present company, I've known some pretty dumb atheists in my time so I doubt the connection is that strong...