Ah, I'm not a medical doctor so I don't know all the ways. But a herpes virus stays, after the infection, for the rest of a human's life. Manifestation can happen after decades or never.

A herpes virus is usually transmitted via contact of mucous membranes so sex, birth, oral sex and even kissing can transmit it. Genital herpes appears in the oral region and oral herpes in the genital region quite frequently.

Your patient might have cought it in his early youth or even as a child. Even an innocent kiss on the lips from parent to child can transmit herpes without anyone noticing and the initial infection can happen without symptoms.