The law of self defense, which is founded in Common Law and is very similar across the country. Seriously, you need to read this book:
Amazon product ASIN 1943809143View: https://www.amazon.com/Law-Self-Defense-Indispensable-Citizen/dp/1943809143
Yes, the victim perceived a threat. Yes, that perception was reasonable. However, the threat did not rise to the level of death or grave bodily injury. You can't shoot someone because they threaten you unless it is an immediate threat of death or grave bodily injury. That is as true in Kentucky as it is in Massachusetts.
You keep throwing this out, but stand your ground was not an issue in this case. All that stand your ground means is that you don't have to try to retreat. That's not the issue here. The crucial issue is the level of threat.
Again, if you shoot someone because they
might punch you and that punch
might kill you then you will be in a world of legal trouble. That is as true in KY as it is in MA.