What does calling a static methods inside the method itself mean in python

Question

I am watching a video on youtube about OOP. I encountered a type of syntax that I could not understand by my past information. The author calls the static method inside the method writing the argument at the beginning of the method's name. The method's function is to detect whether the passed number is an integer or not. The code is below:

class Dog:
    
    @staticmethod
    def is_integer(num):
        if isinstance(num,float):
            return num.is_integer()
        elif isinstance(num,int):
            return True
        else:
            return False

My problem is this:

What is the syntax behind num.is_integer()?