i literally dont wanna pop ur bubble but im pretty sure he didn't stop and stare at ocha bc he realized how much she cares for him bc in that moment there wasnt really conversation between them both to drive to that conclusion.
so to put it in simpler words, he realized that she's putting on a face. bc aint no girl gonna move on from having a meaningful conversation with a villain while fighting THAT QUICK.
the fact that toga sacrificed her life and gave her blood to ocha made her guilty since the original plan was to get toga to change and talk about romance.
also, ocha literally had a near death experience and because of everything that's happened, its natural to fall into a depression. but ocha decided to put on a face instead, a bubbly, happy persona to show she's "okay" when she literally is NAWT. and im like izu too bc she looks like shes doing too much