creating a topmenu item through plugin but ‘is_active’ is not working as expected

I am trying to check for the routename and based on that i want to display the top menu item as active or not. But for some reason is_active does not do anything. Even when i jusst straight up set it to false it still displays as active on the url given in the ‘url’. i want it to only be active when i am on a page where the route name is ‘posts’.

<?php 

namespace DeVriesWebsolutionsPostsPluginBlock;

use MagentoFrameworkDataTreeNodeFactory;
use MagentoFrameworkUrlInterface;
use MagentoFrameworkAppRequestHttp;


class Topmenu
{
    /**
     * @var NodeFactory
     */
    protected $nodeFactory;

    public function __construct(
        NodeFactory $nodeFactory,
        UrlInterface $urlBuilder,
        Http $request
    ) {
        $this->nodeFactory = $nodeFactory;
        $this->_urlBuilder = $urlBuilder;
        $this->_request = $request;
    }

    public function beforeGetHtml(
        MagentoThemeBlockHtmlTopmenu $subject,
        $outermostClass = '',
        $childrenWrapClass = '',
        $limit = 0
    ) {
        $node = $this->nodeFactory->create(
            [
                'data' => $this->getNodeAsArray(),
                'idField' => 'id',
                'tree' => $subject->getMenu()->getTree()
            ]
        );
        $subject->getMenu()->addChild($node);
    }

    protected function getNodeAsArray()
    {
        $routeName = $this->_request->getRouteName();
        $url = $this->_urlBuilder->getUrl("posts/page");
        $isActive = ($routeName == 'posts') ? true : false;

        return [
            'name' => __('Posts'),
            'id' => 'posts_node_id',
            'url' => $url,
            'is_active' => $isActive
        ];
    }
}

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/ObjectManager/etc/config.xsd">
    <type name="MagentoThemeBlockHtmlTopmenu">
        <plugin name="posts-topmenu" type="DeVriesWebsolutionsPostsPluginBlockTopmenu" />
    </type>
</config>