You also see this when people put greasy paper take-out food containers in the recycling. No, it's not recyclable, and worse, it might further contaminate other things and render them non-recyclable as well. But, when I ask houseguests not to put them in our recycle bin, they seem to be honestly startled by the request. Oftentimes they assume it's because I'm a lax recycler and would rather throw things away than sully my pristine recycle bin with uneaten curry.