An example of the compiler generating classes for anonymous functions.

SimpleClass.cs

using UnityEngine;
using UnityEngine.Events;

public class SimpleClass : MonoBehaviour
{
    private UnityEvent _event;

    private void Awake()
    {
        _event.AddListener(() =>
        {
            Debug.Log("Fire!");
        });
    }
}

SimpleClass_Compiled.cs

using System;
using System.Runtime.CompilerServices;
using UnityEngine;
using UnityEngine.Events;

public class SimpleClass : MonoBehaviour
{
  private UnityEvent _event;

  private void Awake()
  {
    // ISSUE: method pointer
    this._event.AddListener(SimpleClass.<>c.<>9__1_0 ?? (SimpleClass.<>c.<>9__1_0 = new UnityAction((object) SimpleClass.<>c.<>9, __methodptr(<Awake>b__1_0))));
  }

  public SimpleClass()
  {
    base.\u002Ector();
  }

  [CompilerGenerated]
  [Serializable]
  private sealed class <>c
  {
    public static readonly SimpleClass.<>c <>9;
    public static UnityAction <>9__1_0;

    static <>c()
    {
      SimpleClass.<>c.<>9 = new SimpleClass.<>c();
    }

    public <>c()
    {
      base.\u002Ector();
    }

    internal void <Awake>b__1_0()
    {
      Debug.Log((object) "Fire!");
    }
  }
}