特地去看了下源码

 append: function() {
    return this.domManip( arguments, function( elem ) {
        if ( this.nodeType === 1 || this.nodeType === 11 || this.nodeType === 9 ) {
            var target = manipulationTarget( this, elem );
            target.appendChild( elem );
        }
    });
}

domManip: function( args, callback ) {

    // Flatten any nested arrays
    args = concat.apply( [], args );

    var fragment, first, scripts, hasScripts, node, doc,
        i = 0,
        l = this.length,
        set = this,
        iNoClone = l - 1,
        value = args[ 0 ],
        isFunction = jQuery.isFunction( value );

    // We can't cloneNode fragments that contain checked, in WebKit
    if ( isFunction ||
            ( l > 1 && typeof value === "string" &&
                !support.checkClone && rchecked.test( value ) ) ) {
        return this.each(function( index ) {
            var self = set.eq( index );
            if ( isFunction ) {
                args[ 0 ] = value.call( this, index, self.html() );
            }
            self.domManip( args, callback );
        });
    }

    if ( l ) {
        fragment = jQuery.buildFragment( args, this[ 0 ].ownerDocument, false, this );
        first = fragment.firstChild;

        if ( fragment.childNodes.length === 1 ) {
            fragment = first;
        }

        if ( first ) {
            scripts = jQuery.map( getAll( fragment, "script" ), disableScript );
            hasScripts = scripts.length;

            // Use the original fragment for the last item instead of the first because it can end up
            // being emptied incorrectly in certain situations (#8070).
            for ( ; i < l; i++ ) {
                node = fragment;

                if ( i !== iNoClone ) {
                    node = jQuery.clone( node, true, true );

                    // Keep references to cloned scripts for later restoration
                    if ( hasScripts ) {
                        // Support: QtWebKit
                        // jQuery.merge because push.apply(_, arraylike) throws
                        jQuery.merge( scripts, getAll( node, "script" ) );
                    }
                }

                callback.call( this[ i ], node, i );
            }

            if ( hasScripts ) {
                doc = scripts[ scripts.length - 1 ].ownerDocument;

                // Reenable scripts
                jQuery.map( scripts, restoreScript );

                // Evaluate executable scripts on first document insertion
                for ( i = 0; i < hasScripts; i++ ) {
                    node = scripts[ i ];
                    if ( rscriptType.test( node.type || "" ) &&
                        !data_priv.access( node, "globalEval" ) && jQuery.contains( doc, node ) ) {

                        if ( node.src ) {
                            // Optional AJAX dependency, but won't run scripts if not present
                            if ( jQuery._evalUrl ) {
                                jQuery._evalUrl( node.src );
                            }
                        } else {
                            jQuery.globalEval( node.textContent.replace( rcleanScript, "" ) );
                        }
                    }
                }
            }
        }
    }

    return this;
}

在domManip方法中找到这行代码

 callback.call( this[ i ], node, i );

这个是往DOM中插入script标签的，不过插入的是这个玩意儿，代码执行到这

这里是当前Element里的结构

这个时候jQuery已经偷梁换柱了，拷贝了我们插入的内容，并修改了类型。类型不对，根本没有当作脚本解析。所以并不会去请求js。
代码继续往下跑，最后执行了这个

 jQuery._evalUrl( node.src );

jQuery._evalUrl = function( url ) {
    return jQuery.ajax({
        url: url,
        type: "GET",
        dataType: "script",
        async: false,
        global: false,
        "throws": true
    });
};

是jQuery自己发起的get请求。到这，这里的随机数字怎么出现很明显了，是ajax里的配置。@Chobits的回答。

以上

https://github.com/jquery/jquery/blob/master/src/ajax/script.js#L25

 $.ajaxSetup({
  cache: true,
});