new 2" drain stack installed - done properly?

Built in 1935, the shower drain stack needed to be replaced.

The plumbers stopped just short of the roof and attached the old galvanized Youngstown pipe to the PVC with a clamp.

Is this the proper way to do it? On the roof, the vent is pretty rusted but I guess it is still holding together. Just not sure they would go through all the trouble of three floors of 2" drain replacement to stop a few feet short of the roof.

That looks to be the right coupling between the two pipes.
A metal wrap to prevent the pipes from shifting.

I guess that was their stopping point, or maybe I can stay it's where the bucks stopped.

My guess is they didn't want to disturb the roof penetration.

John