Bro, the person who created a vow tradition like that must be a pervert
I think it's just the context. As he said, the only way to bring an outsider in was to vow to each other, but Im assuming that traditionally the tribal people would create bonds together and then suggest making a vow, leading them to consummate the proposal and becoming betrothed officially. Which isn't actually much different from other cultures and traditions irl
Novel link?
https://booktoki330.com/novel/5624678?stx=%EB%A7%88%EA%B5%90%EC%A3%BC%EC%9D%98+%EC%B2%A9%EC%9C%BC%EB%A1%9C+%EC%82%B4%EC%95%84%EB%82%A8%EA%B8%B0&book=%EC%99%84%EA%B2%B0%EC%86%8C%EC%84%A4