I can only approach this from the English language, which is why I said technically correct. But I also feel the article should have done a lot better job explaining that they were Dagestani, which is not unreasonable as if this had happened in Chechnya, it would have said Chechen.
Also, I have never seen Russian used interchangeably with Ukrainian, or Belarusian, before or after, 2014. But again, maybe that’s just my English language only bias.
That said, I do appreciate you writing on the explainer for other users who aren’t familiar with the status of, or distinction between Russia and the Caucasus.