The article itself says it's not new.

Where does it say that?

“However, this point of view has been increasingly questioned in recent decades, and a few trigonometric proofs of Pythagoras have made the rounds since then. Claims in the media that Johnson and Jackson’s proof is the first trigonometric proof of Pythagoras are overblown, but their proof could well be the most beautiful and simplest trigonometric proof we have seen to date”

I should be more clear. The article claims that mathematicians have been wondering whether a certain kind of proof is possible. Then author then leads into the actual proof written by the two youths and says that the feat has already been accomplished before and that the novelty of the proof has been overblown in the media.

But the proof itself is still new.