The DotNetNuke Search Admin page is for the management of the internal search indexing, not for search engines such as Google, Baidu, and Bing.
I have found that over time some entries within the search index are old, having lost their prior page content reference.
The search admin page can be used to refresh the references held, ensuring that the content is relevant to searches.
You may wish to consider the items listed under the Ignore Words tab. Adding items here can reduce the number of entries retained in the search index, reducing the size of the database tables and increasing the speed of the website, both in terms of searching and general performance.
If re-indexing the content , on the General tab view, doesn’t flush the old content, or more significantly it times out, this can be an indication that the tables have become too large. You may wish to consider an alternative method for emptying the search tables.