I'm increasingly convinced that a lot of the attacks on Rowling are just pure jealousy from (wannabe) writers who can't bear the fact that they will never have anything like her success. They resent her talent, her hard work and her very fortunate timing in a way that they just can't get past. While obviously some are Potter fans who hate that she's a 'heretic,' I think more are people who may or may not have loved Potter but hate that she has had an unprecedented and probably unrepeatable level of success.
This tweeter has recently released a clearly self-published book. And without sarcasm, well done to them for putting the work into writing a book. That takes dedication and hard work in exchange for no guarantee of a reward. However while I don't want to be mean, "Dust of a Moth's Wing" strikes me as a genuinely awful title. And the summary of the book, the type that would traditionally be on the back cover, is all over the place and incoherent. This person is never going to have Rowling's success and instead of looking inward to work out why, and if they can make changes to improve their own writing, they choose to lash out at someone who has the success they want, instead. Perhaps on some level hoping that starting a twitter spat would encourage JKR's former fans to become R. Ramey Guerrero fans instead. But also to punish her for having what they want, as it's Rowlings fault that they aren't her.