Southern Thailand... Myanmar workers... Muslim rape/murder? Seems likely, not that it helps anyone after the fact.
Burmese workers here are the Thai exquivalent of Mexican/Central American illegals there. Thailand tries to control the border and does deport them regularly, but wages are a lot higher here than Myanmar and there's a never ending and unstoppable flow of them coming in to do manual labor.
That area is not one that has any history of Muslim-separatist terrorism that I'm aware of. It was most likely a straight criminal act. A drug deal gone bad is a definite possibility.
About that very high number of Brits dying here - most are probably suicides of guys that gave all their current and future earnings to their little "tilacs" (darlings) who ran off with them with their Thai boyfriend back upcountry.