mypy why

dog.py

class Dog():
  def __init__(self, name: str) -> None:
    self.name: str = name

  def bark(self) -> str:
    return "Bow-wow (" + self.name + ")"

def test():
  # No mypy error, but causes Rutime error at next line!!!
  dog = Dog(123)
  dog.bark()

test()

# mypy: error: Argument 1 to "Dog" has incompatible type "int"; expected "str"
dog = Dog(123)
dog.bark()

Why not error in line 10?

$ mypy dog.py
dog.py:16: error: Argument 1 to "Dog" has incompatible type "int"; expected "str"