UNESCO is certain to have upset Thai chauvinists everywhere. They have decided that, far from being a Thai tradition, the "khon" dance not only came to Thailand from Cambodia (many Thais regard Cambodians as "country hicks", almost as bad as Lao people in that regard), but it came only via Cambodia. Its origins lie in India. That's a fairly general statement about the origins of many things "Thai". The "wai" for example, is an Indian practice, the Indian equivalent of "Sawasdee" is "Namaste", the Cambodian word for "farang" is "barang". In language I don't place too much reliance on which came first - the Thai word for language - "phasa" - is obviously related to the Malay word "bahasa". And the Thai royal court has Brahmin priests as well Buddhist monks. Although both originated in India they may each have come to Siam via Cambodia - the kingdom centred on Angkor Wat was a Hindu one before it became Buddhist
https://www.bangkokpost.com/news/general/1584418