I was reading through this earlier, and I wanted to note that this is absolutely a Japanese thing and arguably an East Asian thing in general.
Not sure if this is a spoiler(pretty sure it isn't) but:
The phrase used there is
kindan no koi(禁断の恋), which is 1) largely a literary term(almost formal) rarely used in oral speech(and if so, usually in a slightly tongue-in-cheek manner), something you usually see in novels, literary critics, etc. 2) describes the concept/literary trope of "forbidden love" ala
Romeo and Juliet-style, the kind of romantic and passionate love that is shunned/frowned upon by society, which in Japan would include but not limited to(not necessarily limiting ourselves to modern Japan, but the usual contexts in which the concept/phrase gets used to describe when it appears in fiction): incest, adultery, inter-class(rich-poor or noble/royalty-peasant), inter-religional, inter-racial(not necessarily just RL skin-color races but sometimes in fantasy works, actual cross-species stuff; ex.
Twilight would get described as
kindan no koi type of story), inter-national, adult-teen and of course, homosexuality, 3) is usually paired with the other stuff that Hitomi just describes, like being able to communicate thoughts and feeling with each other with but naught a glance because TWUE LUV or something, and 4) in a modern context, is something you usually find executed and described as appearing in teenage romance novels, and usually speaking especially the more trashy/raunchy ones targeted towards a middle-to-upper class, young adult female-audience.
So what does this scene tells us? Well, it first tells us that by using the term unironically Hitomi likes speaking in this pseudo-formal high-class intellectual terms, telling us of a certain type of upbringing; and that she must also read
a lot of trashy/raunchy teenage romance literature directed at rich young girls to immediately (mistakenly) pattern-match Sayaka and Madoka's interactions with the
kindan no koi tropes commonly found in such works.
Make of that what you will, but I think it fits Hitomi's character perfectly, organically, and fleshes it out with very little exposition. My reaction to this scene was to chuckle a bit and say "Ah, so Hitomi is
that type of girl"