re - confusing question...my thoughts to your question are as follows -
According to me the first answer to this question is " I am a human being" Here the interviewer wishes to know whether you are aware of the "Self Concept" It is very essential to know your own "self"...only then can you understand the others.
Here by Self means to be "Aware" of your Physical Self, Psychological Self,social Self Self, Intellectual Self etc..
Here the 5 Ws should be known...Who am I, What am I, HoW, Where and Why. To elaborate further, it is essential to know and be aware of your Attitudes, Beliefs, Habits, your thoughts emotions and behavior, your reaction, impulses etc...It is a whole gamut of "Self Awareness" which is a very interesting and challenging topic.
Hope this brief information would enable you to "think" further and gain more knowledge about your"self'
Thanks and all the best
Sanjay I