No, I think you are misunderstanding the parenthetical claim. They are still benchmarking the actual reimplementation, they are just parenthetically pointing out that the reimplementations are being called from Swift, not Obj-C.

The reimplementation itself is 1.5x to 18x. They are using the parenthetical in precisely the way the style and usage guide suggests, adding the additional information that the new implementation is called from Swift.