It's surprising to you because North Americans have gotten used to saying "people of color" as if they were all united.
Upper-caste Indians basically see themselves as people on top of the racial hierarchy. In many ways they identify far more strongly with British or American elites than with Dalits.
Marginalized people speaking up or protesting bothers people with authoritarian personality traits because those acts are interpreted as attacks upon rigid social hierarchy.
It doesn't really have anything to do with the content of BLM's message, but everything to do with who is saying it, how they're saying it, and to whom.
Upper-caste Indians basically see themselves as people on top of the racial hierarchy. In many ways they identify far more strongly with British or American elites than with Dalits.