As mentioned in the OP article, there are some parents who get involved in the job searches of their young adult children. While I haven't encountered any parents attending a job interview (though I doubt security would let them in the front door), I have received phone calls from parents advocating on behalf of their kids. It is an immediate disqualifier.
I also have a friend who told me she went with her mid-20's daughter on a job interview. She didn't go into the interview, but waited in the lobby "for moral support". I told her that she probably cost her daughter the job.
When you hire someone fresh out of college, you want a person who can think for themself and learn and grow. Bringing mommy to the job interview pretty much says you're not that person.
Of course, it is the rare exception when parents get involved in the hiring process. But it is amazing that it happens at all.
(And to be fair, most of the millennials that I've hired are smart, hardworking, and ultimately successful.)
I've interviewed a few hundred students and/or graduates looking for internships/full-time jobs over the years and I've never heard of a parent being involved in any way - agree that would be a deal-breaker, unless there were some very unusual extenuating circumstances.