Sheet rock on the underside of roof decking?

Has anyone seen this. I came across it yesterday for the first time. On the underside of the roof decking, in the attic, sheet rock is attached. A piece of it broke off and damaged the kitchen ceiling. It’s not over the entire attic, just a part of it. It seems like it would add a lot of weight to the roof.

Townhome?

Yes.

It’s part of the fire barrier between the units. Must be in place, intact, taped/sealed at the seams.

It’s part of the fire separation wall assembly between condo or townhouse units. You did not state the building type, but it must be multi.