No, it is not ethical at all. In any relationship, loyalty and respect are fundamental. Such behavior goes against the values of marriage and monogamy.
One way is to have strict content moderation in media platforms. They should not allow such explicit and inappropriate stories to be published or spread.
He should first stay calm. If he overreacts right away, it could lead to an unnecessary argument. Maybe he can just casually ask his wife about the situation, like 'Hey, who was that person you were posing with?'
Educate yourself about healthy relationships and positive social values. By having a strong understanding of what is right and good, you'll be less likely to be interested in inappropriate content. For example, learn about the importance of respect and loyalty in relationships, which is the opposite of what is implied in such an inappropriate concept.
Watching any form of inappropriate or disrespectful stories about a relationship in a sexual context is not appropriate. It violates the privacy and dignity of others and goes against moral and ethical values.
Well, the husband might want to find out more details about this stranger. If it seems fishy, he could consider accompanying his wife to the place where it happened to inquire. But he also needs to trust his wife's judgment. If she says it was innocent, he should respect that while still being cautious for her safety.
Once, I was on a train and there was an old man who started sharing his adventures in the Himalayas. He told me about how he got lost for days but was saved by a local tribe. He described their unique way of life and the beautiful, unspoiled nature there.