Maybe I missed it in the article, but why would P9 be at a 30 degree angle from all the other planets. Are they saying that what we know of how solar systems collapses to the nearly the same plane is wrong?
It couldn't have formed that far out. We know Uranus and Neptune are too far away - they formed closer in than they are now, and interactions with Saturn and Jupiter pushed them out. In fact, there's evidence that they switched places (Neptune originally being closer). Planet Nine could have been thrown into an eccentric orbit during this time.
Here's a relevant wikipedia article: https://en.wikipedia.org/wiki/Nice_model