Strangest Conversation of the Night

I was just sitting on the couch, minding my own business when an IM popped up on my screen from a username I didn’t recognize. It said simply, “Hi.” Naturally, I responded with a hello in the hopes that the person would explain themselves within the next minute or so with all the vitals, like who they were and what the hell they wanted. Instead, the person asked who I was. I said my name and returned the question in a rather curt manner, pointing out that it was them who messaged me first. “I never sent you any message,” he or she said, “and just responded to yours.” Some back and forth between us and I closed the IM window, bothered. How does one not message me, yet still message me?