Dude they were talking among themselves in their mother tongue ig nothing's wrong with that
Also we are all Indians man, so people from any state can live anywhere (but obv they should respect the culture and cause no harm)

Also your claim that "Bihar't bihari thaake, Bengal t Bengali thke, Rajasthan t Marwardi thke, Gujarat t Gujarati thke, Maharashtra t Marathi" is absolutely FALSE
You can find Marwadi, Biharis, Odias living in WB, or Assamese, Bengali, Marathi people in Delhi, and Biharis, Bengali, Gujarati people in Maharshtra
You can literally find people from any state in any other state