Planning to kill someone like in this is premeditated... agreed?
Non premedidated murder can be a crime of passion, ie not pre planned but committed under loss of temper, in anger etc. For instance, someone might see a yob coining their car and find a brick and crack said yob over the skull, said yob dies. The murder wasn't planned, but done "in the heat of the moment".
Or you and I meet, we talk, you throw a bottle at me, my head cracks and I die. You are sent down for Murder. You didn't plan to kill me, it just happened as I once again set you off. A premedidated murder would be you waiting outside my drive, to catch me walking to work and cracking me over the head with the bottle...
I suspect you knew all this already and just wanted me to take the bait...I did...
This appears to be a little different and taken at an opportune moment.