Its a precautionary step, which sometimes goes beyond control. In this particular case of the Bombay bound aircraft being grounded, it makes sense because the passengers did not listen to the instructions and were arrogant. It does make the atmosphere a bit suspicious and the background for the last two weeks is such that, the air crew had to make a prompt decision, which they did.
A person belonging to certain "racial community" or because they speak in a alien language are not valid reasons, by any means to arrest/interrogate them.
