I find that how "griefer" is defined depends a lot on who is using it.
If you engaged with an unwilling opponent in Open, some would call that griefing because you spoiled what they were doing. Many would call that playing the game the way it was intended.
If you engaged someone in consensual PvP and high-waked out rather than fight to the death, that could be seen as poor sportsmanship. Others would call that playing the game as intended.
For what it's worth, I don't see anything in the video I would consider griefing. You were engaged with CMDR and ship comparable to you and your ship. Looks like system security showed up. When your damage got serious, you high-waked out.
Ask your critics a) how they define "griefer", and b) what you have done to earn that. There might be something to learn on both sides there. (I'm not holding my breath though. Sanity and clear, rational thought don't often appear in any internet forum.)
o7 CMDR