@Kllick
I think they refer to the blonde hairbun, she's showing up in way too many panels coupled with having defined enough appearance.
This author usually don't draw randoms in ways that makes them easy to identify, and rarely drawn fully even if present within a panel.
Just look at the panel showing the two sitting together during lesson for example, except for the blondebun the others are almost stamplike identical designwise.
Try reread ch1 while looking for randoms, notice how they're rarely shown within the panel even in crowded places? How they look pretty much the same regardless of blonde/black?
Compare to current chapter, see how blondebun is properly drawn in pretty much every panel just like any relevant character in any of this authors works?
Will most likely get involved soon one way or another.