There shouldn't be any restricted areas in cities. There's are only 2 locations with restricted areas.

The blockades (biome border) which will unlock the restricted area if you have high enough reputation with the owning faction or if you pay the money to unlock the biome. The doors are locked and closed until you have the reputation or paid. Sometimes an NPC may open the doors at which point a player may walk in by accident. The door should automatically close after a few seconds if no NPC is standing near them. Make sure to look at the lights. If they're red, you should not enter.
Once the doors are open and the lights are green, you're allowed to enter and interact with the trader. If you don't have the rep nor want to pay money, you can break in there and flick the lever in the control room to unlock the gateway yourself, however this turns the station hostile of course.

Pirate outposts may block your access to the armory if you didn't pay the full toll. The door is supposed to be locked, but if an NPC opened it a player may wander in there by accident and cause them to become hostile.

Okay, got it. Guess the player just walked through the door by accident, didn't bother taking a screenshot at the time nor do I remember by memory where such a door might have been right next to the corpse.