The “window” also doesn’t belong to an app! His menu bar continued to show Finder as the active app, not Siri.

Which means, if shipped like this, the Siri dialog will be a poor excuse for a window with:

- no Cmd+Tab, no Cmd+`

- no minimize??

- generally no presence in the Dock whatsoever

- no keyboard shortcuts beyond basic text editing ones

- no smart window resize

- …

So in other words, no Justin, that’s not a window. That’s a resizable Spotlight pop-up with an “X” button.

My guess is that it's deliberate - that Siri window hovers over all apps so that you remain in your current context, and can add files/images/texts from any app to the Siri conversation. There might also be a Siri app on the Mac that was not yet shown.