Inconsistency between different configuration items

The 'Site theme for domain' configuration is utilizing 'radios' widget while 'Admin theme for domain' is using 'select'.

      $form[$domainId][$domainId . '_site'] = [
        '#title' => $this->t('Site theme for domain'),
        '#type' => 'radios',
        '#options' => $themeNames,
        '#default_value' => (NULL !== $config->get($domainId . '_site')) ? $config->get($domainId . '_site') : $defaultSiteTheme,
      ];
      $form[$domainId][$domainId . '_admin'] = [
        '#title' => $this->t('Admin theme for domain'),
        '#suffix' => $this->t('Change permission to allow domain admin theme @link.', [
          '@link' => $this->l($this->t('change permission'),
              Url::fromRoute('user.admin_permissions', [], ['fragment' => 'module-domain_theme_switch'])),
        ]),
        '#type' => 'select',
        '#options' => $themeNames,
        '#default_value' => (NULL !== $config->get($domainId . '_admin')) ? $config->get($domainId . '_admin') : $defaultAdminTheme,
      ];