I think I experienced something similar recently.
A few weeks ago, I was randomly talking to someone in a different department. I had to pass their room to get to where I worked, so I would sometimes bump into them in the corridor, or pass their room with the door open, and I would make the effort to say hi to them.
And one day one of them who was working in our office from an office in a different country came into where I worked and was chatting to a few of us, and he mentioned something about me being smiley and always smiling. And I thought: "Who? Me?"
But then on reflection, I realised that yes, I do make the effort to try to smile and be sociable. It doesn't come naturally to me, so I really do make an effort to seem 'normal'. And somehow that's had an even more positive effect than even I intended.
And now, I recently changed jobs and I'm working in a different department, and today I bumped into someone else, who sits in an open plan area I used to pass, and I used to say hi to him when I was passing. And today we bumped into one another near my new office, and he stopped to chat to me and he said I should stop by and smile again.
Again, I didn't realise that people were noticing. I was just trying to be 'normal'. But people have somehow got this impression that I'm very smiley and friendly! When I'm actually a bit shy and insecure. But in a strange way, it makes me feel more confident. They seem to think I'm friendly and smiley and confident, so I feel I've got to somehow live up to that. And me 'pretending' to be like that... again it's a grey area, when am I pretending, and when am I actually like that?
It's kind of scary, but kind of nice at the same time, that people see me that way when inside I'm more insecure and reserved than they seem to give me credit for.