A plausible reason would be that he was not looking to have an affair but rather was actively seduced. Someone not looking to have an affair would not use a matchmaking service.

Been there done that.

lol I am not the richest man, not even close and nothing physical happened. But I once got into a parasocial relationship after decades of monogamy and no dalliances. Never planned for it, and in hindsight years later don't know what happened. And it was so cathartic.