WordPress – How autoloading classes works even after uninstalled Composer?

I use local webserver XAMPP + WordPress on Windows 10. PHP v.8.2.0, Composer v.2.5.8.

My actions:

1. Installed Composer globally and some package just for initial test to random directory.
2. Copied "vendor" folder to child theme directory(wordpresswp-contentthemestwentytwentythree-child) and
   included autoload.php in functions.php. Made some tests – good, everything works.

Then I deleted almost all files from vendor folder and made some code manipulations. In result, I have folder structure:

twentytwentythree-child/
├── vendor/
│   ├── composer/
│   │   └── autoload_real.php
│   └── autoload.php    
├── style.css
└── functions.php  

functions.php:

require_once __DIR__ . "/vendor/autoload.php";

And this code in autoload_real.php:

class ComposerAutoloaderInit205eb07b158c0f9d7b54b8e32a48421e
{
    private static $loader;

    public static function getLoader()
    {
        self::$loader = $loader = new ComposerAutoloadClassLoader(dirname(__DIR__));

        print "<pre>";
        print_r($loader);
        print "</pre>";

        return $loader;
    }
}

Without any problems I got the printing result on site page:

ComposerAutoloadClassLoader Object
(
    [vendorDir:ComposerAutoloadClassLoader:private] => D:ProgWebXAMPPwwwwordpresswp-contentthemestwentytwentythree-childvendor
    [prefixLengthsPsr4:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [prefixDirsPsr4:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [fallbackDirsPsr4:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [prefixesPsr0:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [fallbackDirsPsr0:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [useIncludePath:ComposerAutoloadClassLoader:private] => 
    [classMap:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [classMapAuthoritative:ComposerAutoloadClassLoader:private] => 
    [missingClasses:ComposerAutoloadClassLoader:private] => Array
        (
        )

    [apcuPrefix:ComposerAutoloadClassLoader:private] => 
)

There is no ClassLoader.php in my folder structure and other vendor autload files, but this code works, and I don’t understand why.

This code doesn’t work on other machine, so I thought about Composer cache, tried to clear it with "composer clear-cache" cli command. I tried change local web server.Then I even uninstalled Composer and pointed out to remove all cache too. No effect, printing still works, I see the same output on WordPress page. So if you know, how without almost all vendor files and even Composer program itself, this code still works with no errors, tell me please.