I always think it's so sad when an artist copies someone else like that. First off--really easy to catch, you just do a reverse google search, and second off--do they really think so poorly of their own art and their own abilities? Everyone comes out worse--the artist who did it, the artist that now has to file a cease and desist and look like the bad guy, the fans who stayed silent, the fans who lashed out...it's just a bad time and it happens so often on twitter. Something must be going on in Art Education because...it feels like a lot of the time it's kids who weren't educated on the subject (and other time it's adults! And that's a different story!)
But when I do style studies (which everyone should do, copying other people's work helps you learn how they did it!), I rarely ever post them on the internet because I don't want people to accidentally think I invented the style. If I ever do a master study--then I try and post who it was that I'm copying (usaully a dead guy). If I reference one photo a lot, I post the photo I'm referencing and I won't sell the art I made off of it if it's too close to the original photo. I'm kind of paranoid about accidentally treading too closely to other artists, especially since I've made a LOT of art over the years and I can't trust if I remember...if it was copying or not. So sometimes I'll see something I REALLY like that someone else does, but I'll give it a hot minute before I implement it into my own work, if at all, and if I do implement it, I make a note that I'll see later.
And like there's also the inverse problem, where some people think they invented everything. I remember on Etsy forums back in the day there was this girl livid that someone else was stealing her idea to make a welcome mat with the word "Hello" painted on it. And like..........no........you can't even trademark an idea that basic, girl, what are you thinking? Likewise I think that certain people have styles that aren't unique to them, but they think it is. Like they do not recognize they are a dime a dozen and it really hurts them when they find out because a fan goes "oh this person is copying the way you paint irises a different shape" and it's like oh boy...here we go again...
But the way I see it, if I'm trying to know if I'm too close to another artist's work, is I ask myself subjectively, would this cause loss to the original artist? Like if I started copying their style so closely and selling essentially their work for less, would that cause a financial problem? And if the answer is ever "yes, this competes with them directly" then I need to step back a bit. Thankfully I've never had to do that, but for things like fanart you do need to reinterpret the original concept enough that it is never going to make a loss for the original artist.