Death-cap mushrooms are native to Europe and first identified on the east coast of North America in 1897, and on the west coast in 1938. They do not appear to be native to North America.

The article is mostly concerned with their spread into British Columbia, probably from the root balls of imported European sweet chestnut trees.

Although we've seen a lot of non-native invasive species above ground--tumbleweeds and starlings come to mind--the article is a fascinating framing of the question (voiced in the article), "What does it mean to move a tree-root mushroom to a distant continent?"