Well it is a cosy set of numbers for atheists - but I do worry about these kinds of social research statistics (having been involved with a lot of market research.)
The first problem is that many people who report they belong to a religion are in fact (if you could force them to be honest) nonbelievers conforming to family expectations and peer pressures.
I reported on census forms that I was RC for at least a decade after I was a thoroughly lapsed Catholic and for a further decade after I knew I was agnostic.
So quite a number of those "theist" criminals may actually be in our camp
Second problem is that atheists are a motley crew. I have found that only a small few take a genuine interest in reason and morality to the extent they become courageous enough to in-principle identify themselves as atheists.
But many nonbelievers just don't give a shit about anything much - not even about being atheist - and certainly not stating openly they're atheist and having to deal with all the questions and prejudice that comes from the faithful. It wouldn't surprise me if a nontrivial proportion of the 20% jailbirds who don't respond are actually nonbelievers, what I'd probably label lazy atheists.