[yumraj]

Don't you have a process where you ask the basis for both yes and no?

Both yes and no need to be substantiated by examples by the interviewers and that should be able to tell you whether there is any bias or not.

[anonymousJim12]

Yes, they do provide a basis. In this case the basis was weak and lazy, though that is the style of work I've come to expect from working with this person.

[paxys]

IMO that should be concerning regardless of the caste angle. Throw out their feedback, raise this with their manager or HR, and recommend that they go through interview training again.