Fiber and Copper are two completely separate modes of transmission. Although they do interface all the time, they can also be completely independent. If you're in Windstream copper territory, it's totally possible that AT&T has purchased right-of-way to install their own Fiber for future AT&T services, not Windstream services.
Being in a Windstream landline area just means they own the last mile copper facilities. Other carriers can still build-out their own Fiber networks within that territory. However if those carriers want it to interface with Windstream copper to a customer premise, they would pay a lease for that right.
If you're in a residential area and AT&T is laying Fiber, chances are it's for U-verse or FTTP/FTTN. OR it's just crisscrossing the neighborhood to reach a large commercial building.