That “update” from Artstation doesn’t really mean anything, it’s basically the same message they send out a few weeks ago already.
Unless Epic actually sues Stable AI and Midjourney, these new terms won’t change anything. Neither does artstations new opt-in “no-AI” html-tag, the AI tools will scrape the images regardless of html tags or terms.
So this is just a meaningless attempt to calm down the anger of the artists. Which is even more obvious when you consider that Epic - as you pointed out - still allows these AI images to be sold on their Unreal marketplace or even the artstation marketplace. The irony.