This article left me wondering what do they mean by the term alien planet? Aren't all planets simply alien by default, or do they mean planets outside our solar system are alien? Do they mean there is alien life there? Is this a a new keyword the astronomy community is using to generate more buzz and get more attention to their articles?
Very interesting article!. The term alien planet is not a scientific one, so I think you already answered your own question by saying that it was used in the article to generate more buzz.
In the English language the word is used to describe something that's not familiar, so you could argue that this is in fact an alien planet, but because of the subject in question being an exoplanet I would bet they did this as a technique to get more attention.