The accused killed someone with a firearm during a spontaneous confrontation. That's the basis of the 2nd degree murder charge. Self-defence is something that can be raised at trial by the defence. Then, the Crown has to prove the contrary.
Remember, too, that there is a clear political bent against firearms use for self defence against people. In the days and months following the May 2020 OIC and both iterations of Bill C-21, the PM and Ministers Blair and Mendicino have all said that "we don't arm ourselves for defence against our fellow citizens" or words to that effect. So, my guess is that this isn't as clear-cut as initial reports make it out to be. So, yes, it's possible the Crown thought "let's err on the side of politics, lay the charge and let the courts decide". A lateral pass of a political football.
I'm going to postulate that it's unlikely, as a PAL holder, that the accused was a sh!trat, But there is definitely a lot more to this that we don't know yet.