Why did he watch the video after slapping her husband?

Because you didn't make him comfortable, didn't make him feel good, he couldn't be satisfied, maybe it was the kind he had a strong desire, maybe it was his personal preference and habitual sex life. That kind of video can satisfy his desire. Watching that kind of video is just to satisfy his desire. He thinks that kind of video is much better than yours. It looks interesting, but there is nothing to see. No big deal. Don't make a fuss.