Further, the term "arrest" would be factually incorrect. India has a concept of detention — police can legally detain any individual on suspicion (even without a warrant/crime) upto a period of 24 hours — post which the detainee is presented to a magistrate where the detention can be legally challenged.
> a court in Kokrajhar denied him bail, ordering him to be held in custody for three days
Instead of an actual arrest this seems to be an extended detention (approved a court).
> arrest coincided with the arrival of the British prime minister
> He was taken across the country to Assam in India’s north-east
Considering these statements, instead of being arrested for his tweet, the context makes it seem more like the police felt he could be a threat given the arrival of Johnson, and they decided to preemptively detain him in a far corner of the country.
Regardless of whether I'm correct or not, it won't be the first time this has happened.
((Please ignore the typos/formatting, I typed this on a phone))
Edit: Just saw the article also mentions
> In the capital, Delhi, bulldozers have demolished the homes of Muslims accused of rioting
While this is true, it also needs to be mentioned that Delhi is not under BJP government (the ruling party).