Confusion 2

This story is just my continuation. As what I've said from my previous stories, I will squeeze every experience that I had.

There was this one night when I couldn't sleep. I was browsing the internet and decided to turn it off around 2am. For me it was still too early so I decided to go to the living room where I usually sleep. That living room can be converted into a bedroom. There are six people in our house. All five sleep upstairs while I sleep downstairs. I closed the sliding door and switched off the remaining lights. Darkness filled the whole house. Lying on my bed, I turned on my phone. It was 3am. I was watching a Korean gag show when I heard some footsteps on the stairs. I saw a shadow going down. From where I was located, you can see whosoever will go or down from their hips down to their feet because of the transparent glass wall. I suddenly stopped and pretended to sleep. I knew it was my grandmother because she usually walks slowly. I was afraid that I might be scolded again for staying up late. I slightly opened my eyes and noticed that shadow walked really slowly. I heard the bathroom's door open. Crossed eyebrows, I wasn't able to move and a lot of questions were going through my mind, "why doesn't she turn on the lights? Why did my brother\'s cousin let her go downstairs alone?" I couldn't wait any longer and I turned on the lights. I called her, "grandma? No one answered. I decided to go outside the living room and I couldn't see anyone there. The dining area was empty as was the bathroom. Puzzled by the thought of that shadow, I went back to bed thinking this time it was for real.

The next morning, I kiddingly told my aunt about the shadow I saw last night and I told her it's an old person [I just felt it, I just knew it is an old person, I don't know why]. My aunt was not laughing at all but she looked surprised. She then told me that her husband's father stayed in the room across our bedroom upstairs when he was ill and died in the hospital after leaving that room. He was 86 years old when he died. She even told me that our maid told her that there was this old man roaming around our house. I couldn't explain what I was feeling at that time. In addition to that, the stairs are between those rooms.

I wonder how come I know that it was actually an old person or did I just guess it right?