Why is he complaining?

I am a very quiet and reserved person. There's this guy who I like and works in the same section at work. He is confident and easy-going and likes to talk with everyone.

We don't talk much. Yesterday, he tried to strike up a conversation with me but at that given moment I was extremely busy. He asked me a closed-ended question so, I answered his question, didn't know what else to say, and continued working. Few moments later, I heard him talking with his friend (who is also a coworker) nearby, where he complained that I always cut the conversation short with him. He could see that I was very busy, so why was he complaining?

Why is he complaining?
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