Hmm, Ive pondered this a lot. Ochi is 12 and Isumi is 18. It seems unlikely that Ochi would be attempt to undermine Isumi psychologically.
At least to start with, its kind of an accident after a remark he makes about Touya and all that's already in Isumi's head.



Then when he sees the result he starts to rub it in, which looks really evil.

Or is it just his proud self?