Did this ever happen to you?

I was at one of my company's events recently and I was listening to a presentation. Some guy came and sat in the vacant seat next to mine. From my quick glance towards him, I figured that this is someone I know pretty well. I turned around and looked at his face. From the side view, I was quite confident that I know this person. I tapped his shoulder and said "Hi". He turned around and from the front, he looked quite different. He was not the person I thought he was, I had done a mistake. However, by this time this guy was in the game. From the looks on his face, I could easily tell he was totally confused inside and was trying to guess who I was. He of course tried not to show it on his face and replied "Hi. How are you doing? Which project are you in now?" What could I do? I too acted as if I knew him and exchanged pleasantries. At the end of the day, he must still be wondering who this stranger who spoke to him was.