Something eerie happened

I was staying back last night to OT, it was almost 930pm when Colleague A came and ask me if I am going off. There was still another 2 colleague at the other end. I was still deciding weather to continue stay or go home. In the end I decide to go off with colleague A. Packed everything and went downstair with colleague A, we did not awitch off the lights as there are still people a level 2. If we are the last person to go off, we would need to switch off all the lights.

While we were at level 1, the office lights at level 1 are still on, colleague A went in to see who is still there, I follow too. Colleague B was still working.

Colleague A: Oiii….you still don’t want to go home ar?

Colleague B: Going off soon, another 10 mins, you all go first.
Colleague A: Ok.

Colleague A helped me to call cab while I call my senior to inform her I going off liao, as its 930pm and no more reports coming in. We walked to the main gate to wait for our cab and Colleague B called Colleague A saying she going off now and wait for her. While waiting for colleague B to come out, colleague said to me: "She siao one, left her alone downstair she still don’t want to go home." When I heard her say these words I was abit shocked.

I remember seeing another guy inside too, he was sitting at the desk at the end face facing down doing his tihngs, looks very busy, cant see the face, only his head and hair. He looks abit like Colleague C. Than colleague B join us, I notice she switch off all the lights on level 1, I looked at her.

Me: Why you off all the lights? Still got a guy inside.
Colleague B: What? No people inside, only left me alone.
Me: No, when we go in look for you, I saw a guy there, looks like colleague C.
Colleague A: No, when we go in only left her, no guy inside only her alone. Colleague C went off at 5:30pm.
Colleague B: Only me alone! I got check no people liao than I off all the lights!
Me: But I saw a guy sitting down there, if not colleague C than who is he?
Colleague A and B: Maggie your cab come liao..go..go…quickly go home.
Me: errr….ok…

I keep thinking I really saw a guy there, why both of them no saw him? Something wrong with my eye? Maybe my eye got problem.....maybe....