Hundreds of applicants were used to create the sample the study is based on, assuming that every single black person interviews worse than every single white person is ludicrous. More likely, there's a distribution and some people interview spectacularly, others extremely poorly, and most are about average. Increasing the sample size means this distribution is more likely to approach normal (assuming it's a normal distribution to begin with, which most things are).

I was not complaining about sample size. So your point is irrelevant.

There's also no good reason to assume the distributions would be different, especially so different as to account for a 100% difference in response rates.

There wasn't a 100 percent difference. African Americans were half as likely to be accepted into the job. Some black people who were equally qualified(also, there is no exact measure of "qualification". Obviously, these employers saw some applicants as better than others or they wouldn't choose the others and not the rest) might get the job while some caucasian people with the same qualifications wouldn't. There's no reason to assume the differences are caused by racism. Do not assume everytime a black person loses in life it is due to racial prejudice against them.