Where do you see that it isn't true? Clicking through to the MicroSlop site, it looks like it confirms this as true:

The Microsoft 365 Copilot app (formerly Office) lets you create, share, and collaborate all in one place with your favorite apps now including Copilot.*

Is this just a wording fail and the app is changing, not the product line?

If so, still not even the most confusing rebrand in recent memory.