Sourcing it is fine. The rule indicates that the user in question is passing it off as their own. Citing a source ≠ plagiarism (unless there's improper citing).
Citing the source is one thing but copy/pasting should be assessed on a case-to-case basis.
I've seen some users simply copy pasting news articles on coindesk and pasting them here without any attempt at discussion at all. If this goes unchecked pretty soon you could have bots using forum keywords to search for online articles to copy paste here.