It is worth noting that even for a West coast Europe is very maritime because in addition to the Atlantic it has the North Sea and Baltic kind of in the middle of it, and the Mediterranian to its South. And because people (including this article) like to take either Spain (sitting on a peninsular) or Great Britain (an island) as points of reference. And the (upper half of the) US East coast is very continental even for an East Coast, because of the effects of the Rockies mentioned in the article.

But overall the point the article tries to make is that people like to say that Europe is unusually mild when really people just compare it to the wrong places (with the US East coast being a popular and uniquely bad comparison du to the reasons summarized by GP).