How does trick or treating remind junior of rowdy

From the text:

But I just felt stupid and naive after those guys took off. I lay there in the dirt and remembered how Rowdy and I used to trick-or-treat together. We'd always wear the same costume. And I knew that if I'd been with him, I never would have gotten assaulted. And then I wondered if Rowdy was one of the guys who just beat me up. Damn, that would be awful. But I couldn't I believe it. I wouldn't believe it. No matter how much he hated me, Rowdy would never hurt me that way. Never.