Black silhouette

My friend has a brother who's now in his thirties. When this brother was 15, a mysterious thing happened to him.

One ordinary summer day, his parents left the boy home alone. It seemed like nothing could happen to a 15-year-old boy in an apartment. But later that evening, something happened that no one expected. The boy ran out onto the balcony as if scalded and started screaming at the top of his lungs: "People! Help! Help, they're killing me! Someone, get me out of here!" The people on the street were terrified: everyone thought something bad had happened. Someone quick-witted called the fire department (I don't know why, though). The fire department soon arrived and rescued the boy from the balcony. He was terrified and shaking. He remained unconscious for several hours, but eventually told his mother what had happened.

 It turned out that in the evening, while he was quietly watching television, the room slowly plunged into complete darkness (even though it was still light outside), and the boy suddenly began to experience an all-consuming, primal fear. At that moment, SOMETHING appeared from the depths of the hallway, emitting sounds similar to flatulence. The boy described this creature as the silhouette of a very tall man, seemingly composed entirely of black smoke. The silhouette approached, and the young man was frozen with fear—he wanted to run, but he couldn't. Then, when they were only a few steps apart, he overcame himself and ran headlong to the balcony, while the silhouette, approaching a sunny window, melted into thin air. Incidentally, it was later discovered that in the places where the silhouette had moved, the linoleum on the floor had turned black, as if charred.

For many years now, his friend's family has been wondering—what was it? But they are unlikely to ever know the answer.