No incidents are detected with a keyword that is present in a web page.
Network Monitor can capture the HTTP GET requests, which contain the URL that the browser is loading, however, it does not capture the response, which contains the content of the Web page.
This means that the DLP Network Monitor will not detect content that is present in an external Web page when it is loaded by the browser. This would normally be accomplished with a web content filtering solution not a data loss prevention product.
Monitoring of the HTTP GET requests for the Network Monitor servers can be enabled by following the article linked below: