I think Ernesto definitely had all kinds of complicated and hidden feelings suddenly rise to the surface in that moment. After all, he and Héctor had spent their entire childhoods together, they had a lot of good memories. If Ernesto’s spent nearly a century trying to forget what he’d done, who knows what kind of nostalgia suddenly blindsided him at seeing Héctor’s picture, the living face he’d gone so many years without seeing.
Of course it couldn’t last too long, Ernesto’s spent too many years lying to himself and others for his facade to crumble that easily, but who knows, maybe for that brief moment, that picture reminded him of the good he’d had, not just of the evil he’d done.