I experienced something weird

I went out to pick up my food order , the delivery person was a little late, when i looked at the wall of my building,
I saw a shadow that seem to be walking on the wall and when i looked back no one was there, it was very strange .
I looked back about 5 times each time the shodow figure seem to be walking but no one was there ??? So the delivery guy's car showed up and i got my order , looked at the wall one more time and no nothing was there anymore