Isn’t this the moment Sakurai realizes his feelings towards Youichi?…then after this Inoue gives Sakurai, Youichi’s photograph and he actually recognizes that Youichi is quite beautiful >///<
Hmm, I think up until this moment in the following chapter (ch5)
he was still very much in denial about the true nature of his feelings.
However, I think that was the first time he actually paid closer attention to Youichi and got flustered by him! Which was very cute and so much like Sakurai.
What I really love about that scene is that even though they were both constantly snapping at each other, there was also this certain tension between them that has actually existed from the very beginning and in a way separated them from being potential buddies or enemies. And they were both aware of it too ("Are you curious about only my painting? Or curious about me?" oh how I adore Youichi for saying that)! I'm pretty sure they were so mean to each other because of that tension, not the other way around.