(Note: If you have Office desktop apps already installed on your Windows 10 device, you have to uninstall them to see these.)
These Desktop bridge versions of the Office apps are not the same as the Universal Windows Platform (UWP) versions of the Office apps that were in the Store. Microsoft officials said last year that they intended to reposition the UWP Office apps as Office Mobile apps recommended for phones and tablets with screen sizes less than 10.1 inches.
Microsoft made these Desktop Bridge apps -- which company officials previously referred to as the "Office in the Windows Store apps" -- available to Windows 10 S users in preview form last Summer. Later, Microsoft also included some select testers in the preview.
Microsoft execs decided to port the core Office apps using the Desktop Bridge for a couple reasons. They wanted to show other software makers that bringing even complex Win32 apps to the Store was possible and useful when it comes to security and upgradability. They also wanted to signal that, at some point, the Store will become the sole vehicle via which Microsoft plans to make its Office apps available for download to customers.
I've asked Microsoft for more on the Desktop bridge versions of the Office apps in the Store and any further details the company is willing to provide about these apps. No word back so far.
Update (January 25): A Microsoft spokesperson confirmed the rollout. The official statement: "Microsoft is currently in the process of rolling out Office 365 apps into the Microsoft Store. If you've already have an Office 365 consumer subscription, this means you can now install from the Microsoft Store and take advantage of rating and review options."