I guess the burden of proof is on you at this point. So I would suggest to try what I do when I'm looking to see who copied content. Highlight 2 to 3 consecutive sentences and click search. The results will be on target for the first 3 to 5 results and after that they are usually very disconnected and way out in left field. If you have more than I think it is 10 to 15 words that are in one result, I was told it was duplicate content.
Highlight 2 to 3 consecutive sentences at least 5 times throughout your hub - so you get 5 different sets of sentences from different places in your hub and put them in search engines - pick more than one search engine - I use Google and Yahoo. The results are usually quite different.
In some cases, all you have to do is change the wording so it is not so similar to what you found in the search results.
In other cases, it is a case of spacing out the text and interjecting photos or videos.
If you are quoting someone and you have linked the quote, unlink it. Just cite it in text form.
If you are quoting someone and you are using word for word for more than 15 words, cut it down to 15 words. Citing sources is good, just don't link them if you have more than 15 words in the quote. The roaming robots don't understand quoting quotations at all so every one of them is called duplicate content and the Mechanical Turk workers don't know duplicate content from a quotation so they flag all of the hubs that quote. Most of them anyway. My 9/11 Spotlight hub got flagged because I quoted a bunch of people. My choices were to either remove the quotes or cut them down to 15 words. I cut them down and removed the links - instant publish w/no duplicate content flag.
So do the searches first, then take a closer look at the way you wrote the hub and quotes.