What exactly constitutes a "flawless victory/defeat" in TF2?

I'm just curious as to what these messages "actually" mean. In one case, we played a long hard battle of Dustbowl, and eventually the timer ran out.

Then, the Administrator said: "Flawless Defeat! You didn't kill anyone!!".

I was extremely positive I had at least killed one person. So why did this message show up? What exactly triggers a flawless defeat/victory?

I'm pretty sure something is wrong with the server setup.

Flawless defeat is when you lose without any of the opposing team dying in arena mode. Likewise flawless victory is when you win without taking a single casualty.

My guess is that the conditions for this is if everyone is alive on map end, and so on a non-arena map this happens regularly. The server must think you're playing arena and so is playing this sound.