For Columbia College, an interview is not a required step in the admissions process. A few applicants will be interviewed by admissions officers, but most may or may not get an interview with a local alum. The local alumni clubs run this. Some areas have more applicants than available alumni interviewers, so many applicants don’t get an interview.
The admissions office says a candidate’s chance of admission will not be affected by not having an interview. To me, this means logically that they’re not even reading the alumni interview reports. It’s a mechanism to keep us connected and in a mood to donate 
As of today, with the ED notifications due out next week, for those applicants it’s too late to do interviews anyway.
GL to your son. He has no reason to worry from not having interviewed.