A creepy thing that happened once

About 3 years ago, I was taking a walk around the block. In front of me was a person with short, red (dyed) hair. This person was carrying a backpack and a binder despite it being June. I thought nothing of this at the time. As I continued walking, this person swerved to the right (towards a house I have passed many times before). I thought at first that this person was simply visiting the house, as I knew that nobody that looked like this person lived there. Things got strange when I realized that this person had somehow gotten from the front of the house to the back of the house in only a few seconds (something that would not have been possible, even if this person had been running). I turned around (I was literally still right next to the house, just a few steps away from where I had previously been) and walked into the alley next to it. I looked around for this person that I had seen and could not see them anywhere. There were no signs that they had been there at all. To make things creepier, my sister saw this same person two years later. This time, however, they were walking in the alleyway between my house and another house. My sister watched this person (same backpack, same shirt, same red hair) walk towards our shed and then disappear entirely. This person seemed to have just vanished behind our shed.