I'll cut to the chase.

Married man grew up with this other woman in the same town since childhood. She's an old friend (never had any relationship beyond that). Their parents know each other and are friends. She is also married. She's in the man's neighborhood for a while visiting...wants to meet with ol' buddy, man friend and talk about old times. So...they meet once in a while and go out for dinner, coffee, etc. to chat.

Wife knows what's up, family (man & woman parents) knows what's up...all acceptable. However,...in-laws and wife's friends find it totally unacceptable.

So in Korea...

A man who goes out with a woman (old friends)...is that a date?
A married man out with a woman (old friends)...is that dating & cheating?
A married man occasionally meets with a woman (still, old friend)...an affair?

I'm under the impression that in Korea, a man must unconditionally cut all ties with the opposite sex, completely...no female friends allowed! Whether they have dated in the past does not matter at all. Some sort of culturally evolved paranoia?

Funny, though...do they believe it is "safer" for a married man to hang out with another man? Most likely they'd end up going to some place where sex sells...can't really do that with a female buddy

That's because it's not the sex the wives are worried about. Many older women are okay with their husbands infrequently visiting prostitutes, especially if it's because of their jobs. However, going on dates and building up a friendship or emotional bond is considered cheating. It's all about the family and marriage contract. Husbands are not going to leave their wives and children for prostitutes.