I don't think the issue is so much plagiarism, as in direct lifting of her material, as him trying to make a profit from publishing an encyclopedia of her work.

Not if you read the reports of JKR's testimony.

If the issue were publishing an encyclopedia for profit I don't think the balance of fandom opinion would be on JKR's side. Nor would the lawsuit have got this far: a true encylcopedia would selectively quote from her works and would be fair use. (Which, yes, is the defence they're using.)

But the evidence so far presented suggests that he's plagiarised much, much more than would be acceptable under fair use provisions, and added very little of the original content needed to make the lexicon legally an original work. Perhaps the evidence is wrong; I don't know. The lawsuit was prompted by the profit issue: she tolerated his infringement as long as it was confined to the web. But it's not the central issue of the case...if I understand it correctly.

And that pie chart is wonderful, ain't it? (Even more so if it's accurate.)