I gather it was a number used by Mr. Marit in his dissenting opinion. There's no precise indication of exactly how it was calculated.
Judge Mills was asked by the media where it came from, because he's of course the keeper of the documents and all the representations, records, and so forth. He provided the quote you just read into the record. In the same article he goes on to say that the calculation must have been based on including some of the representations that were received, but not all of the representations that were received, including a number of form letters that were submitted without briefs.