This is a clear duplicate, and a vote or flag to close would have been the thing to do. We also prefer citations to be much more brief, and much more obvious. E.g.
According to {link_to_user} on {link to answer}:
(short bit of supporting text)
Additionally, cited content should not make up the majority of an answer. The bulk of any post a user writes should be their own.
With that being said, I think the user posting it had the best intentions at heart, and just didn't quite realize how things work. If you look, a link back to the original answer was present even in the first revision. I honestly think they were trying to be helpful by trying to summarize your answer. The question itself has been subsequently and appropriately marked as a duplicate.
When you see a clear case of plagiarism, where even an attempt to give credit to the original source isn't made, it's definitely something that should be flagged and we take it quite seriously.
In this case, it really wasn't plagiarism, it was just someone answering a question that they really should have flagged, while not quite understanding how to cite other answers properly. Still, this should be brought to a moderator's attention - it's a clear duplicate and a mod needs to see the answer in question.
In either case, use the 'other' reason and provide as much context and information as you can.