That use may not be idiomatic (in the sense how, say, an Indian or Chinese mainlainder would never describe a civil war between white people on US soil as 'ethnic tension' in the English language) but it's a valid use of the word from their POV.
I dislike non-idiomatic uses, as idioms have their uses in language, and not all idiomatic usages are inherently racist or sexist. (Does the word 'white flag' connote something bad? Or does the phrase 'as white and pure as snow' mean something derogatory, as it does not include other colours?)
The phrase 'ethnic tension' to me usually means some arguments between factions in a failed government, local militia forces, autocratic regimes with many tribes, etc. I don't think use of such idioms should be governed. It is definitely censorship.