Oh you are not a patient?

One of my night shifts: I am standing in front of a ward bureau because
I had to ask for some drugs for a certain patient.
The bureau is locked because the other night watch is in a patient's room.

All of a sudden there is an old female patient standing next to me.
She asks: "Why didn't you just gave the alarm? You could have stayed in your bed!"
I look at her, pretty surprised, she starts laughing.
"Oh, well, you are not a patient?! You are one of the nurses! Haha!"
She continues laughing and goes away.
I feel amused and somehow a little bit weird.
I've never been seen as a patient until now.