The article is discussing a technique used to dispose of waste plastic. In other words plastic that would exists in macro and micro form regardless of its use to improve roads.
It seems from the article, they have considered that and concluded that since plastic becomes part of the bitumen, and does not exist as plastic particles.
Unless it has chemically changed considerably it's a problem. My impression is they are saying "don't worry, chunks aren't going to break off because it's melted into the bitumen" and are wholly ignoring the micro scale.
That would be an improvement considering the garbage situation in India.