That may be the case for much of anime in general, but there's nothing in this particular image, just taken on its own, to say it's the sex flush. It certainly doesn't require the artist to have an understanding of physiology, even if their style is influenced by the entirety of anime in general (and how could it not be?). First of all, the only part of these women's skin that's really visible and would also flush is their face, same as a blush, and like you mentioned, the sex flush tends to include the chest but also other parts of the body, even the hands and soles of the feet. You can't differentiate a flush and a regular blush from just the face. In fact, you can't even really differentiate unless you have seen the same person in both circumstances because different people flush and blush in different ways. The sex flush tends to be more extensive sure, but plenty of people blush on their whole face and some people flush just a little bit on their cheeks. But all of that is immaterial because they are also clearly wearing makeup like eyeliner so there's no reason not to think they're wearing, you know... blush as well. Also, the sex flush doesn't just occur in women by the way, it's just a bit more likely than it is in men.

I don't want this comment to be taken as a "well ackshually" kind of thing, but I'm making it because some people in these threads have been cherry picking things that might seem sexually suggestive to them and using that as evidence that this image is sexualizing the subjects in it. But all it really is is a drawing of conventionally attractive women. That's it. I am all for having a strict rule against any horny posting, but this ain't that.