I'm studying the C# constructor and destructor with Unity, but I don't know why it works like this

I’m studying C#’s Constructer and destructor with unity component system.
I’m sorry if the English of this question is weird. I used a translator cause I am not good at English.
The log output came out like this.

1. The Constructor log was displayed without pressing the play button. Why?
   
2. When I pressed the play button, I saw a log of something being created and immediately disappearing. I didn’t write a code to create an object after the game started, where does this phrase run?

This is my code.

project working structure

Pressing the space bar brings the pre-made pre-fab to the game world,
and Prefab has a component that attached to test the constructor and
destructor.

CubeFactory.cs / when Press the space bar, It creates Prefab.
this component was attached to "GameObject" Gameobject

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class CubeFactory : MonoBehaviour
{
    public GameObject obj;
    private int pos = 1;
    void Start()
    {   
    }
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.Space))
        {
            Instantiate(obj,new Vector3(pos,0,0),Quaternion.identity);
            pos++;
        }
    }
}

ClassTest.cs / Component for Testing Constructor and Destructor. It attached Cube prefab.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ClassTest : MonoBehaviour
{
    public ClassTest(){
        Debug.Log("I was born!");
    }
    ~ClassTest(){
        Debug.Log("I Died x0x");
    }
}

This is my project file. (I’m sorry to compress it up. I haven’t learned how to use Git yet.)<
https://github.com/Scincy/UnityStudy

  void Start()
    {
      Debug.Log("I was born!"); //Will be called when the gameObject is active for the first time
    }

public GameObject cube;

    void Update()
    {
        cube= GameObject.Find("Cube(Clone)"); //Depending on how your object is called
        if(cube == null)
        {
         Debug.Log("Either not created or is destroyed");
        }
     }