It is really hard to see your point, because you attacked a competent anaconda, alone from that should tell you this is someone who traded and is used to a trade conda at best, especially given that you have combat experience, you knew this. Then there's your reddit post with video, specifically titled murdered. And you don't see yourself as a griefer? In general those that 'laugh' over kills like that or seek gratification from it, which it seems you do, are those I quality as griefers.
And of course he is going to deploy hardpoints, you interdicted him, that is an aggressive action of course he is going to try defending himself. And of course he is going to be upset you attacked a person who was trying to help his brother, for no other reason then "hey there's an anaconda"
I don't know what you were expecting, it is a very normal reaction to such things happening.
The whole "Don't play in open" mentality makes no sense, because at best it pushes people away from open, and I do not believe open is meant to be a paradise for those that grief people.
You could easily have banged them up a bit and then left, your advantage was pretty clear early on in the video, so you could have left with no problem and it would still have been a win.
Anaconda makes a great trading ship better then T9 by most accounts, so why wouldn't someone be flying that for trading?
That said maybe if there was a pvp activity measuring or such stat for systems, hotspots, allowing people to get an idea of how dangerous it is to go to a specific location, then I could agree, but how would people know as it is now?