Well it clearly is and you saying it cannot be considered plagiarism is just wrong. I don't even know if that was the post you were actually banned for but it's plagiarism regardless of what you and a couple of others may claim or think.

I know of one case where someone was banned for plagiarism in the recent massacre, but a very careful reading of the context showed that the person actually did just forget to quote, and by "quoting" the post they were expressing an actual point even if it constituted their entire post. This person was unbanned without any sigban, since this isn't plagiarism.