Okay, I'm glad that you've admitted that it's real steel, and not some "vaporized" or "dustified" byproduct.
You're making progress, TS!
Now, you say the material in the Zafar photo is "drifting" to the north. However, videos show quite clearly that most of this material is plummeting to the ground, impeded only by the air. Please watch some videos and tell me if you agree.
Videos and still photos show these large sections of steel trailing lighter debris and dust as they fall. Do you agree that this is what we're seeing in the Zafar photo, not only on the northwest side, but all around the building? If you're unsure about that, watch videos and look at photos of both towers, such as the images of the large south tower sections falling past and into WTC 3. Note the falling perimeter sections trailing lighter dust and debris.
Okay?
Now, as for why the steel wound up where it did, try this experiment. Place an empty aluminum drink can on the floor. While wearing shoes, step on the top of the can, hard enough to crush it. Do this with six cans, aligning the labels in the same orientation each time before stepping on them.
Take notes on how the can collapses differed from each other, and develop a hypothesis about those differences.
Report back.