I think the percentages are just a percent of your total score - so vehicles = 5% ...well that's just 5% of your overall score - mine is around that and I can tell you I'm not in the 5th percentile. haha.
The stat missing to me is headshots. I have 100 headshots insignia and 100 sniper headshot insignia quite a while ago and I have 600 kills. So, I think the majority of my sniper kills are headshots (which is good because at distance, body shots don't kill)