It's an interesting result with an unjustified conclusion and an utterly inappropriate title.
The unjustified:
"So, the scientists figured that the plastic itself would contain something that makes it tasty.
"When plastic comes from the factory, it has hundreds of chemical additives on it. Any one of these chemicals or a combination of them could be acting as a stimulant that makes plastic appealing to corals," said Alexander C. Seymour, who co-led the study with Allen."
There's no reason at all to assume there is a soluble chemical on the plastic that they "want".
The fact that most plastics are hydrophobic likely makes it look like things they think are edible. Fat's, many proteins, natural energy storage molecules such as polyhydroxybutyrate, etc, are quite hydrophobic, and in nature, nearly everything that is hydrophobic is organic and can potentially be a food.
The title? Junk food? No, it's more like eating the wrapper, not the junk food inside. Vodka and vinegar are the junk foods we feed our tanks.
