Employment is one of the most important material facts. Having a job, and the type of job, is a significant indicator of whether you will return to your home country after using the visa. If you're unemployed, your visa application will almost surely be rejected, unless you're a minor or a full-time student or retiree or being supported by a spouse. If you're in a crappy job, you'll also have a difficult time getting your visa approved, although not as bad as if you were unemployed. If you're in a job that pays very well, your chances are very much improved, because they expect that you won't want to leave that good job to become an illegal immigrant in the US.
He probably was a 19 year old claiming to be a consultant at IBM. Or something else just as obvious that the original consular officer should have caught but didn't.
Still it does not make sense. The consul who issued teh visa did not catch this. The GC adjudicator did not catch this. And all these two persons are supposed to review the employment claim more carefully than the IO who review N400. Then suddenly the IO now caught this during a brief interview.