China claims jurisdiction because 20 Chinese citizens were murdered, if that’s what you’re wondering.

They are usually Chinese triad gangsters who operate scam businesses and illegal casinos in south east asia.

https://en.wikipedia.org/wiki/Triad_(organised_crime)

They are Han Chinese, Most of those triad family come from Yunan borders a few decades ago. In Myanmar , thanks to military junta , they can easily buy citizenship by bribing authorities One of them is even a MP Senate in Military aligned party.