Cyborg was used to people not seeing him as human. Little girls were scared of him, little boys thought he was just a robot and nothing more.
So when a couple of kids hit him playing baseball, Cyborg expected them to run away in terror. Which is why he was surprised when they declared him their hero and showed off their own prosthetics.
Nothing changed in the grand scheme of things, people still thought he was a freak or a monster. But for a moment in time, Cyborg could slip away and be just Victor Stone, and feel human again.