The reason that Bud always introduces himself as Bud and not Buddy is explained in chapter 5. Bud is telling the reader about his mother and some of the things that she told Bud when he was younger. She told Bud to always remember that his name is Bud, not Buddy. She said that if she wanted him to be called Buddy, she would have named him that. His mother also explained that a bud will someday be a flower. It is just waiting to come out and be beautiful. She told Bud that he is like that bud and flower. He is waiting for the right time to finally open up and show the world exactly who he is. She also makes a nice joke that "Buddy" is a dog's name. Below is the text.
"She had four favorite things to tell me, one of them was about the picture and another one was about my name.
She'd say, "Bud is your name and don't you ever let anyone call you anything outside of that either."
She'd tell me, "Especially don't you ever let anyone call you Buddy, I may have some problems but being stupid isn't one of them, I would've added that dy onto the end of your name if I intended for it to be there. I knew what I was doing, Buddy is a dog's name or a name that someone's going to use on you if they're being false-friendly. Your name is Bud, period." I'd say, "OK, Momma."
And she'd say, every single time, "And do you know what a bud is?"
I always answered, "Yes, Momma" but it was like she didn't hear me, she'd tell me anyway.
"A bud is a flower-to-be. A flower-in-waiting. Waiting for just the right warmth and care to open up. It's a little fist of love waiting to unfold and be seen by the world. And that's you."