As
@franknd mentioned, Mr. Mullen is probably the most useful member of this forum. Your son should take him up on his offer. At a minimum, he will provide insight into the DoDMERB process your son underwent (what happened and when) and provide a final answer as to if there is anything that can be done at this point.
As an aside, I joined this forum on 10/6/2020 when my son was going through the academy application process. He had gotten his DodMETS referral and when he called to make his medical exam appointment, the provider told him that their earliest available appointment was in March of 2021, five months later! As a non-military family, we didn't know if this was normal, but I was worried about it as it seemed like too long to wait and so I started Googling. This forum popped up in my search so I joined and posted about the situation asking if that kind of timeframe was normal. Enter Larry Mullen who advised that I read about parent/applicant separation of duties and have my son email. My son sent the email as suggested and Mr. Mullen sprung into action using his undisclosed superpowers such that by the next day, my son had a new provider with an appointment set for two weeks hence. It is because of his intervention that in December of 2020, my son was able to get a full appointment offer to the Coast Guard Academy (he had applied EA) instead of one conditional on medical clearance.
I work in a field where clients sometime utilize paper applications. There are parts of the application that are in red, rather than black ink. The purpose of the red is to highlight that these sections are important to read carefully; the red has nothing to do with mood. While I cannot claim to know what is in another person's head, I suspect that's why Mr. Mullen chose to reply in red. If anyone scrolls through these responses, his will stand out, demonstrating importance. Truly, as it relates to DodMERB, Mr. Mullen is the absolute authority. Best of luck to your son, wherever his path leads.