ARCore compatibility with iOS platform

Here Google ARCore team says that we could create AR experiences that Android and iOS users can share: ARCore support for Unity developers  |  Google for Developers.

But what exactly does it mean?
Does it means I could use GoogleARCore namespace and all associated code(classes, structs, methods, etc) to write an IPhone game using ARCore sdk?

Yes, that is correct. Under the hood, the ARCore SDK for iOS uses ARKit for the underlying AR functionality. The regular (non-Unity) iOS SDK quickstart page provides more details about the functionality on iOS:

Note that you could also use Unity’s own AR Foundation instead, although it doesn’t include the cloud anchor functionality that the ARCore SDK provides.

For now Arcore supports only cloud anchors on iOS platform other features like plane tracking, light estimation etc will not work.