I didn't really think to think in depth into that but hmm, I think that maybe he was being apathetic in that he knows that Seishin is lost to him. Like after the scene with Kyoko, that was the absolute end of their friendship, or so Toshio thought. "That sounds like him" is almost sad, like "we were friends, and I still know you all over" but it'll also never be the same because their friendship line is basically cut already.

Or we can look at it another way and say that since he's decided to devote his near future to hunting Shiki. He sacrificed his wife, and now if he has to lose Seishin too it's like 'so be it'?