Why would he respond back if he is not interested in me?

A year ago I met a guy through a friend who was just visiting. We got each others numbers and was texting everyday while he was in town. We were still talking when he left but only for a couple of weeks then he stopped talking to me. I was confuse thought he was interested in me and he acted like he did. Recently I send him a message how he was doing because I was curious if he would replied back. I was shocked that he did and thought he wouldn't. I was doing all the talking and he kept asking me how I was doing. He read my message and never replied back. If he wasn't interested in me why would he respond to my message?
Why would he respond back if he is not interested in me?
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