Yes, it's a defence mechanism used by people who feel the need to behave aggressively towards others in order to protect themselves. If someone says "I don't care what you think", it means they DO care what you think but they really wished they didn't. If they truly didn't care, they wouldn't even bother responding.

By the way, sorry this comment originally got posted multiple times. There was a temporary problem with Medium and it looked like my comment wasn't being posted.