Of course they're not. They're destroying goods that they can't sell at a profit because, for example, the cost of processing some unworn but returned goods outweighs the potential profit from those goods.
In TFA it's estimated that between 4% and 9% of clothing put on the EU market is destroyed before being worn. An admittedly high uncertainty, but even 4% of all clothing sold in the EU is still a heck of a lot of clothes.
Even if most of the energy goes into kinetic energy of the air, that air will lose momentum via turbulence and friction with the surrounding air, which will end up as... heat.
On a side note, this site reacts to window size changes (phone rotation portrait <-> landscape) with a really nice animated shuffle of the content. It's more visible on the "Sentences" page linked in another comment [0]. I've not seen that before, and certainly wasn't expecting it on a site that is otherwise pretty no-frills.
In TFA it's estimated that between 4% and 9% of clothing put on the EU market is destroyed before being worn. An admittedly high uncertainty, but even 4% of all clothing sold in the EU is still a heck of a lot of clothes.