I looked at the article on iMore, very poorly written (IMO), just uses a lot of technical jargon and really doesn't provide any good examples. It seems the article assumes that you are already a practiced user of the shortcuts app on the iPhone/iPad.
However, they have some short video clips from users showing shortcuts that initiate actions on the HomePod, but the music playback example just initiates an Airplay stream from an iPhone to the HomePod using a third-party app called Overcast (I think, although as I said earlier the article isn't very well written).
I'm guessing that the Overcast app just has it output (on the iPhone) preselected to the HomePod and they have Siri shortcut support in Overcast to run requests for content playback.
In fact, it appears that you can do the same thing using Apple's Music app as long as you've preselected the audio destination as the HomePod.
So, from the iPhone you can say, "Hey Siri, play the song 'Don't Let Me Get Me.'" and that will play on the HomePod (that command also puts up a dialog on the iPhone asking to open the Music app, but you can ignore that and the song still plays).
However, I wouldn't be surprised if the above also works on iOS 10 with Apple Music, even without shortcuts. So, this may be nothing new and the iMore article seems (?) to suggest that you can't initiate a shortcut from the HomePod to play something via the Overcast app (which makes some sense as the Overcast app is on the iPhone, not on the HomePod).