Was it conquest? you can get a lot of points for catching flags (450 if the enemy alreay had it). Healing, ammo supply, supression, spawn point etc can all count. 8k does seem high for a low kill count so I would not expect to see it too often. I personally
get a lot of vehicle disables and destroys but not often the kill/s.
I dont know if extra xp gets added onto the scoreboard score or after the match? But i got 1 kill and had 5 deaths last night and scored over 4000 points (on the scoreboard before extras) , battlefield isnt all about the K/D ratio is good that way , promotes
teamwork and going for the flags/mcoms
Marking the objective (aim at flag/MCOM while over 100m away and press select, a diamond effect should appear around the flag name) can increase your score quite a bit, you get double points for resupplying/healing and extra points for defence and kills
while in the flags radius (when it centers itself annoyingly on your screen).
You have to mark the objective from a good distance away and it can be kind of glitchy whether it wants to do it or not.