Wow, the fact the author actually had to explain the obvious to the butthurt masses
They had to explain because they did a terrible job of presenting what they meant to within the actual manga itself. Usually when a panel is in someone's imagination there are FX or something to give any hint whatsoever that this is the case, which the author did not do.
Even if it's in his imagination, nothing about the scene makes sense. Supposedly it's just about food right? Say that's the case, what living creature outside of symbiotic beings allows themselves to be fed on by a stranger casually like that? Oh, that's right, none of them. And it's just about food and not sex right? So why does the vampire not feed on men too, and only females? Why mostly human females, when Genjin seem to (for some inexplicable reason) be so accepting of getting fed on? Even the one genjin he seems to approach is one of the most popular ones in the school, that has a fan club, and when he goes to her class to get her contact info (a play on the trope of the popular playboy hitting on the FMC), he doesn't try to get any of the other people in classes info? Why does he bother feeding on humans at all, when it just creates drama and Genjin are supposedly so accepting, if it's just about food?
Literally trash worldbuilding, all an excuse to put in his NTR fetish bait, that even if the imagination panel wasn't terribly executed and actually understood by the majority of his audience STILL doesn't make sense in terms of the logic of the world he's haphazardly creating.
Author is going all in trying to do this big brain cultural differences complex worldbuilding, instead of just sticking to comfy slice of life romcom, and fell flat on their face because they weren't up to the task.