Either there are not enough kills to go around or the opponents do not show, if you do not register a kill or a death on the scoreboard, the statistics make it out to seem as though you were not present at all, even if you spawn and flip flags.
Edit: Actually, this may only happen on battles where there are no enemies. Just did a 0-0 game which gave me a score and it counted.
Re-Edit: Just finished a battle with a no-show enemy team and got a 0-0 score. Not entirely sure if the bug was fixed or if there was some other kind of an issue.
Not really a big deal but thought I'd mention it.
Forgive me if this is in the wrong section or already a known issue, did some searching and couldn't find anything.