With that low of numbers, the random number generator can screw you over pretty easy. With only two attack, you have a one in three chance of missing entirely. With two defense, you have a one in three chance of your defense failing completely - and when that happens, the defense suffers attrition regardless of whether it stopped an attack or not.
On average, your ship would take 9 turns to kill the 2/0/0 ship. Their fleet would take an average of 12.5 turns to kill yours, so reloading and trying again many times would give a range of results, from what you saw to you killing two of their ships. Killing all of them is possible, but pretty unlikely.
Since you only attempted the battle once, you probably saw a few bad rounds that killed your ship before you could catch up with what was statistically expectable. For instance, you have a one in 9 chance of rolling double zeroes for attack/defense each round. Their fleet has a one in 24 chance of getting 5 damage on the same round. If both occur at the same time, you've accomplished nothing while losing 20% of your HP. Basically, you suffered several bad rounds.
