Mirrored Glances After Class: Coincidence or a Silent Signal?

It was when the lecture

has ended and everyone siting beside me left the hall, only a few people lingering around, some getting ready to leave the hall. I was siting far behind row at the end of the lecture hall alone, with no-one beside me or behind. I was looking at the projector screen in front with my laptop on my lap, then this girl that I spoke with a few times (we are not close friends or anything), walking to the exit in front of me from a distance

and her head was looking towards at me. I caught her eye and I looked down, I too noticed she looked away, and then I looked up again, then she looked at me again, I looked down again, she looked away again, I looked up again, then she too looked at me once again until she exits the hall.

It was like she was mirroring my action and this happened so fast in seconds. What was that about?