I might be wrong but I think that one of the major job of a plagiarism tool is to check if a content is already available on the web and through that info one can investigate to know the original author...the tool checked the content and discovered that it was already on the web which happened to be your own content and you are obviously the original author ....the only issue I have with the tool is that it is supposed to help give the link to the posts which it found so that way one can easily know the original author...but what the tool just do is "hey I found a similar content" and it ends....the developers of the tool should work more on it....though I have a feeling that the feature is available but not for free users but available to premium users I lguess...
RE: How to detect plagiarism