You might have spotted him tending plants on his apartment balcony and such, but once he heard about the eruption of normal people suddenly becoming raving madmen, he found for some reason he didn't want to go out as much. Didn't want to risk running into someone like that.
Because if it turns out normal humans can flip out and become raving, bloodthirsty maniacs, it just further proves the point about the Gestalts -- and about how monstrous his own actions were.
He can't stay inside forever, however. Eventually, he has to go out to get supplies. These grocery stores are an odd thing for him compared to the normal markets, but he supposes they're convenient enough. Notably, he's not got any of his weapons on him. Doesn't want to have to do anything he'll regret later.
He's done that enough anyway.*