It is quite confusing indeed. But this is probably an exception to solve conflicting logic behind other status like allied, federated, neutral and war.
Guess you can think of peace as 'you won't fight this guy but won't help him either. want to stay out of anything to do with this guy.' You can probably take a solace in the battle not turning into HD vs Astrum. It instead was LN vs Astrum so you lost nothing except time and some gold you need to pay to get your damaged equipment repaired.
