It was a super buggy battle, I couldn't move all of my ships there, and I was attempting to land two Outposts a couple hours earlier on seperate planets in the same system. When I logged back in 20 minutes later all of my ships were gone and he had placed Outposts on the rest of the planets, and that's when I noticed the fighters all around. I'm chalking it up to a weird bug, Hopefully losing the 8 destroyers and two outposts doesn't put me too far behind three days in!