Is it possible to graduate from medical school without obtaining a specialist certification?

‌My mother recently mentioned that she is acting as a matchmaker for someone she knows.
A friend's son graduated from medical school, but he isn't practicing as a doctor, hasn't obtained a specialist certification, and is currently running a business.
Is it possible to graduate from medical school but not get a specialist certification?
He is in his late 30s, and it is certain that he graduated from a decent medical school in Seoul, but they say he isn't practicing medicine.
When I mentioned this to the woman's side, they asked if that even makes sense, so I am inquiring here.