Which category do you belong?

It was my first day with new job so I was mentally prepared to handle new role, responsibilities, colleagues, boss. Surprisingly, I was warmly welcomed by everyone during a departmental get together that elated me, however, what disturbed me to even greater extent was a question which I had to answer for at least 10 times that very day. I had never imagined that people would be asking me "Which category do you belong?", clearly showing their interest. Obviously 'Disturbing' for me because it is my first Government sector job & it compelled me to think on present scenario and pros-cons of this prevalent system.