This shows where it listed 6 spartan kills, yet I had 7 alone with a Rocket Pod turret. It also shows a positive KDA with 6 kills and 8 deaths so there has to be something wrong here.
It is kind of confusing. AI kills are counted in the weapons count, in addition to spartans. You likely killed a marine. KDA is positive because AI kills are counted as part of the total kill count. In that game it looks like you killed 8 AI + 6 generic kills. Total of 14 kills.