Why use past perfect when the story is told chronologically?

Question

I'm struggling to understand the logic underlying the use of tenses here even though I know pretty much about the past perfect tense (basically, saw all uses in several grammars and several articles on this site but came up short).

He swept the door shut behind him. It banged loudly. He leaned back against it. The piano HAD COME to a stop, and his mom’s voice floated to him: “What was that?” “Sorry, Mom,” he called back.

More context: I suppose the chronological order of events should be as follows:

1. He shuts the door.
2. It bangs.
3. He leans against it.
4. His mom stops playing the piano.
5. His mom asks: "What was that?"
6. He answers: "Sorry, mom"

Why would anyone use "had come to a stop" instead of "came to a stop" here?

Furthermore, it says in here: "Several past events described in succession are usually expressed by the simple past. But if an earlier completed action is mentioned among them, such an action is often expressed by the past perfect."

"If the actions happened one after another in the past and are enumerated in the same succession, the simple past is used, not the past perfect. For example: She packed her suitcase, put her ticket, passport and money into her handbag, and called a taxi."

Answer 1

Because the sequence is not necessarily as you've listed it.

What it's telling you is that when he leans against the door, the piano had already stopped. Probably he was so busy running out that he did not notice the piano stopping; but when he pauses and leans against the door, he notices that it has stopped. This use of past perfect carries the reader along with the protagonist's perception of time.