After the Hour of Joy. Boxy Boo saw you a work left alive but he saw you so scared...he let you live...in fact. He always stayed in his jack in the box state so you wouldn't be scared of him but when a toy was about to kill you when you weren't looking...he would quickly take care of it...he protected you...until he came out of it and you seen him.

Boxy Boo: "Calm down. I've been protecting you. Never met you but you made me feel bad so I'm keeping you safe."