How is java.util.Calendar an example for factory method design pattern?

Refactoring Guru provides a good example for factory method.

In that example there are Common product interface, Concrete products, Base creator and Concrete creator. But in Calendar, I find only Common product interface (Calendar class) and Concrete products ( GregorianCalendar, JapaneseImperialCalendar etc. which extends Calendar).

We call Calendar.getInstance() and we get instance of Calendar. My expectation was that we call a concrete creator and get an instance of concrete product.

How is Calendar an example for factory method?