Not very useful because they don't specify what they mean by mathematician.
The job market for mathematicians isn't that great, but computational stuff might be ok. I have a PhD in topology, and it's pretty useless for getting jobs. Actually, the issue here isn't so much that I can't get a job. I probably could if I was any good at getting jobs. The bigger issue is that the jobs all have nothing to do with what I studied. Most of the former grad students I know who got jobs in industry are just doing straight software development type stuff, with not a whole lot of math involved. I know several who just have completely standard programmer jobs, and some who do some machine learning or data science.
Computational math might be different, though--I don't know. And not only that, but I believe that someone who spends graduate school with an eye towards getting a job in industry the whole time and learning the appropriate skills, beyond just the name of the degree, will have a much better chance of finding something.
The exercise I recommend is to do a mock job search to see what's out there. It's hard to find very clear statistics about it because the stats don't really tell you the full story. For example, the 2012 AMS statistics say that close to 1/3 of math PhDs got jobs in industry, but I'm not sure if there is data on what they studied specifically, and whether or not they are doing something totally different from what they studied in grad school. I think for most math PhDs, it really is a career CHANGE when you move to industry.
If you search for math jobs on Indeed or something (not that Indeed is necessarily a fair sample, but still), you get a lot of actuarial jobs (which generally turns out to be only a math-flavored job, rather than a math job, they'll think you're overqualified if you have a PhD, and if that weren't enough, the entry-level market is totally saturated, so it's really hard to get your foot in the door), data science, and some quantitative finance stuff. You'll come across some engineering jobs, too, but usually, when you look at the detailed requirements, it tends to become clear that although they will accept a math degree in theory, they are really looking for more of an engineer. So, that's why I'm sort of scornful towards my degree right now and feel like I wasted my time, even if I do get a job, even if it's high-paying and so on. But, in theory, if you get internships and stuff, you might get the kind of contacts and experience you need to qualify for a more suitable industry job.