So I think there is a bit of unfortunate wording and lack of context in this article.

the "Shouldn't exist" quote doesn't seem to be attributed to any scientist or fisherman, and I suspect is an editorial comment from someone who associates coral with the tropics.

Have a look at species like Paragorgia arborea or the Primnoisis corals, which are both common in BC waters, and even in Alaska. Much further north.

Even in the article they indicate that the threats to these species in our waters are increasing temperatures and interactions with fishing gear, because they are cold-water, low-light corals.

Lessons of the day:

Cold-water, deep sea corals exist.

They aren't here because of global warming, but they could be threatened by it.

Because of where they are, they are poorly understood and reefs of them are still being discovered.