(I discussed this in Discord and I will put here what we've discuss in light of the carnage and the storyline later)

The theme centered around loneliness and finding meaning in otherwise meaningless task. The horror is the vagueness of the massacre.

Basically, this is a good idea.
I wait for the article to know what kind of data they find in this facility's computers, just to realize what was its purpose, how did the owners had robots several decades ago and what could be the cause of this carnage.
Oh, and: would you explain me why this "Cafe du parc" title?

The Authority discovered an abandoned underground laboratory. When they entered the facility, they discovered a sole inhabitant, a sentient worker robot. When interviewed, the robot revealed that they are an only person left after the workers and other robots are massacred. They don’t know how or why it happened.

Since the communication signal is unavailable and it cannot go outside due to them shutting down if they do so, the robot decided to spend their time doing manual labour like usual, including conserving what remains in the facility. This is a way for the robot to curb their loneliness.

Because of their conservating for roughly 50 years, the Authority managed to document bits and pieces of the facility while making speculations on how it happened. But due to the robot’s inability to go outside, they have to stay but also received visitors every once a week

The theme centered around loneliness and finding meaning in otherwise meaningless task. The horror is the vagueness of the massacre.