It looks like the author of the article was using Wireshark to intercept network traffic. In the article there is a screenshot of a window with the title "follow TCP stream" and a headline "Stream content", exactly like in Wireshark.

I have used the same trick sometimes when nobody could remember the FTP credentials, but they were stored in the FTP program and a connection to the FTP server was still possible. Sometimes the guy with access to the admin panel is just not available, so a possible solution is to use Wireshark to retrieve the password, which is usually transmitted without encryption.