Big wave of posts over the last day or so, all of them quoting this post, which says, in part:

With Apple’s annual Worldwide Developers Conference (WWDC) inching closer, Siri has revealed plans for Apple to give the assistant a “brand new voice”, most likely as part of its iOS 12 release.

As discovered by Nathan Simpson when users ask “Hey Siri. Tell me about WWDC”, Siri responds with “La la la, Siri is getting a brand new voice!”.

And in this associated post, they say:

As discovered by The Apple Post on Monday, when users ask “Hey Siri. Tell me about WWDC” the assistant responds with a couple of different answers, however, the most interesting is when the reply implies of a new “meshey & matte” home for Siri.

First things first, these Siri responses are from the leadup to WWDC 2017, when the HomePod was first announced. Seems like Apple neglected to tweak Siri for this year’s WWDC, leaving those old responses in place, waiting to be rediscovered.

I gave Siri the exact same query, “Tell me about WWDC” and invariably got some form of “You can get all the details on Apple’s web site” with a button to take me there. So this seems fixed now.