This is just my personal opinion, but based on the covid-19 epidemic and how it’s affecting universities, your son may want to consider concentrating more heavily on the job market - especially if he does not want to do an online master’s. Many programs are switching to hybrid or online-only models to reduce in-person physical contact between students (and thus transmission of the disease).
I’m not in computer science. We can’t really weigh chances for graduate programs, but his GPA and GRE scores make him a relatively strong candidate. He’d probably want to get at least 1-2 recommendations from CS professors; 1 recommendation from a person in a related field who knows him very well and has supervised him in research would probably be fine. (But it depends on the field - I’m in psychology, and while a recommendation from a sociology professor with overlapping research could be really good, a recommendation from an art history professor wouldn’t do much for us because our methods and theories are so different.)