I love clips like this that completely remove all context. The building was on fire for hours. If you watch the entire collapse, you see parts of the building collapse at different times. The fires were so intense, flames were shooting out of the windows like a blowtorch. Gigantic chunks of the other two towers pierced the building like swords.

The best part of this is that even if one believes jet fuel burning for many hours led to the collapse of at least one of the buildings (I don't buy this argument), in the basements of the collapsed towers where the 47 central support columns connected with the bedrock, hot spots of "literally molten steel" were discovered more than a month after the collapse. Such persistent and intense residual heat, 70 feet below the surface, in an oxygen deprived environment, cannot be explained by combustion. On the other hand, thermite contains its own supply of oxygen and does not require any external source of air. Consequently, it cannot be smothered, and may ignite in any environment given sufficient initial heat. It burns well while wet, and cannot be easily extinguished with water—though enough water to remove sufficient heat may stop the reaction.

In that gif, you can see the sky through the windows on the top floor on the left side; the building is already collapsing when that gif starts. In slightly longer versions of that clip, you can see the change occur in those windows: https://youtu.be/PK_iBYSqEsc?t=15

Your gif starts approximately 8 seconds too late.