It doesn't even need to be the case that there is a difference in mental capabilities between races. It could be that certain groups have a culture that leads them to be better or worse at certain tasks on average, and those groups can be predominantly of one race/ethnicity. It could be that some cultures cause people to be overconfident in their abilities (e.g. causing them to be more likely to apply for jobs they are unqualified for).
Or more desperate to get a job, making more of them apply for positions they don't match, or pad their resumes.
Or have worse connections, not getting headhunted to jobs, making relatively more of them apply for jobs than natives do.
Or have less resources and means, making them pick from the bottom of the barrel when choosing recruiters; the type that pads resumes and work on the redneck duck hunting principle (fill the sky with lead and you'll hit something), instead of taking time to search for employers that are a good match.
In either case, if 80% of applicants to a job are from somewhere, it doesn't mean that 80% of qualified applicants for a job are.
And it doesn't imply discrimination if a large amount of them get turned down. That some are, indeed, hired, goes a long way to hint at it being merit that lands the jobs.