JavaScript ES6 - mixins with super

mixin.js

// This mixin might be used to extend a class with or without its
// own "foo" method
const mixin = Base => class extends Base {
  foo() {
    // Only call super.foo() if it exists!
    if (super.foo) {
      super.foo();
    }
    
    console.log('mixin');
  }
};

class BaseWithMethod {
  foo() {
    console.log('base with method')
  }
}
class myClass1 extends mixin(BaseWithMethod) {}
console.log( (new myClass1).foo() );
// logs:
//   base with method
//   mixin

class BaseWithNoMethod {}
class myClass2 extends mixin(BaseWithNoMethod) {}
console.log( (new myClass2).foo() );
// logs:
//   mixin

Why do you consider this a 'mixin' rather than just plain old inheritance?