If you read that blog post fully, it says that you can't connect to Hangouts with XMPP. See also: https://developers.google.com/talk/

"We announced a new communications product, Hangouts, in May 2013. Hangouts will replace Google Talk and does not support XMPP."

You can still connect to Google Talk (not Hangouts) with a third-party client, but Google has not kept up with developments in the standard (particularly the requirement for server-to-server encryption) and is no longer interoperable with most other providers.