Why does Abstract Factory use abstract class instead of interface?

Question

I am learning about design patterns and the first example in the book is about Abstract Factory. I have built the exercise in VS and all looks good, but there is one questio

Answer 1

"Abstract" in "abstract factory" has nothing to do with "abstract" in abstract class. Abstract factory is "base" for concrete factory, but design pattern itself does not enforce any particular implementation. Abstract factory can be abstract or even concrete class, interface or some form of duck typed object depending on language you use.

Indeed in C# interface is very reasonable way to specify Abstract Factory.