Redshirt designation

I'm not good at "why" questions about other people, but I can assure you that how he is listed on the roster this year does not affect his eligibility next year. 

If your son didn't play his freshman year, it counts as a year on the five-year clock but not as a year of competition. It doesn't matter whether he was kept out because of medical reasons or because he didn't earn playing time.

With regard to what is commonly called a medical redshirt, the decision to request a waiver belongs to the school, not to the player. In your son's case, there is no need to request a waiver.  He still has one year of eligibility and one year remaining on the five-year clock, so he is on track to participate four years of competition without a waiver.

If he gets hurt next year, the decision to request a waiver could come into play.

As swampboy said what is listed on the website, press guide, etc. is immaterial.  If he didn't compete at all in a season he is eligible to be a redshirt.  But that decision is up to the coach.  Its up to the school/coach to determine when to redshirt somebody.  Even if he didn't play the coach does not have to consider him a redshirt.

About the only one who can answer your question would be the coach or athletic office at the school.