That's bizarre. You should post that as a bug report. It's especially weird because the results indicate you destroyed all three Thalan ships.

Draws result when both sides have fired a large number of times without either being victorious.  Consequently it goes into sudden death with, as you can see above, each ship firing for much more damage than usual until one side is completely eliminated.

At least, I think that's what is going on there.

It's because the Thalans had Battleships, while you had frigates. Battleships can take a good bit more damage then your frigates despite the defense upgrades. Happens to me all the time.

Now I've experienced a draw, too.

The game then returned to the main screen where I saw the Persuader (the Korx ship) was still alive with 12 hp. I had to attack it again to finish it off.

Thanks to tech inflation and "slow" tech speed, defenses in this game were always much higher then attack. All of the Korx ships of this class (which I always renamed as they never went in fleets) were particularly tough to kill. My guess is that when a battle lasts long enough, it's automatically declared a draw. Thanks to TOA tech inflation hitting weapons worse then anything else, I have a feeling this may become more common.