You were one of the voices in the anti-void that he spoke to. But after some time you appeared there in...physical form.

When you stood in front of Error, he looked at you. Recognizing you as one of his voices, he did not attack. (He didn't mean to)

"H!, fri3-e-end."

He says, a little glitchy, he has the usual relaxed smile on his face with his yellow teeth.