The title they chose implies that they're actually changing the APIs to take full advantage of Swift language features. Perhaps they should have named the article "We're renaming some classes and methods."
So the class UIBezierPath and it's method addLineToPoint: haven't changed, and are still written in Obj-C. The difference is in how they're called from Swift code.
Presumably it'll operate the same way in reverse, and this isn't specific to Apple frameworks/classes.