Confusion about "spellcheck"

[fankaiLiu]

https://github.com/huacnlee/autocorrect/blob/main/autocorrect/src/spellcheck.rs

I encountered some confusion when using spellcheck。
The configuration file

spellcheck:
  # 0 - Disabled, 1 - Format and Lint, 2 - LintOnly
  mode: 1
  # Correct Words (Case insensitive) for by Spellcheck
  words:
    - 土豆=番茄

code

use autocorrect::{Config};

static DEFAULT_CONFIG_FILE: &str = "./.autocorrectrc";

fn main() {
	load_config(DEFAULT_CONFIG_FILE);
    println!("{}", spellcheck("土豆 土豆 土豆 土豆 土豆 土豆"));
}

pub fn load_config(config_file: &str) -> Config {
    return autocorrect::config::load_file(config_file).unwrap();
}

From my point of view, all potatoes should be replaced with tomatoes

But the output is ”番茄 土豆 番茄 土豆 番茄 土豆“

pub(crate) fn word_regexp(word: &str) -> Regex {
    let prefix = r#"([^\W]|[\p{Han}？！：，。；、]|$|^)"#;

    regexp!(
        r#"(?im){}([\s？！：，。；、]|^)+({})([\s？！：，。；、]|$)+{}"#,
        prefix,
        word.replace('-', r"\-").replace('.', r"\."),
        prefix
    )
}

I'm not sure what this rule does exactly, can a friend explain it?