Yeah, basically. Premeditated aggression is usually instrumental, but reactive aggression can be planned to a degree as well, particularly in your case considering he wasn't around you when he heard about your boyfriend, and thus he couldn't react immediately. But the fact that he was motivated by anger toward a perceived threat and it was an interpersonal conflict between close family members point to reactive aggression.

Like you mentioned, it isn't that cut and dry, as people are multifaceted and can have both emotional and financial reasons for doing any one thing, and their thoughts/behavior don't always fit neatly into the different subtypes of aggression.