^^ Well, yes it is.
Homicide legal definition of homicide
https://legal-dictionary.thefreedictionary.com/homicide
Homicide. The killing of one human being by another human being. Although the term homicide is sometimes used synonymously with murder, homicide is broader in scope than murder.Murder is a form of criminal homicide; other forms of homicide might not constitute criminal acts.
That's why they call it 'justifiable homicide'.
Self-defense
The use of force to protect oneself from an attempted injury by another. If justified, self-defense is a
defense to a number of crimes and
torts involving force, including
murder,
assault and
battery.
Homicide can be one of many results from defending yourself. You can shoot some one with a gun in self defense, which is the example he used, and it not kill them.
Self defense is not homicide, it's not even an action, it's a justification for the use of force. If you kill them while defending yourself, It's the reason or defense of why the homicide took place, which if proven leads to a justifiable homicide. But the justification (self defense) or the reason such force was used, in itself is not homicide.
Edit:
I will admit, in responding to him, I was purposely playing on his words.
Why?
Because he believes that taking another person's life is an acceptable solution and ok, if you can find the means to justify it. (History is full of nut cases who in their mind have justified those they have killed). Then attempts to defend that belief using the example of shooting someone in self defense. But does shooting someone, even if he believes it's justified as self defense, equal a homicide? No! Because the act of shooting someone does not mean you killed them, nor does the act of defending one's self mean you killed them.
His own poorly worded example shows that self defense is nothing more than a justification for the use of force, where the result of that force, lead to a homicide.
If self defense meant homicide (one human killing another human), the definition would say the use of force to kill another human, meaning death is always the end result. But it doesn't, it says the use of force to protect ones self from harm. Which is why the definition of self defense is just a justification for the force used that resulted in a homicide. So again self defense is not homicide. Killing someone is homicides, self defense just justification for the force used.
Sorry for the long drawn out response.