That’s no problem. The official description of Bioshock directly from the developers is

Deadly weapons in one hand. Brutal powers in the other. Fight for your life and uncover the mystery or Rapture in the remnants of this utopian city gone wrong.

This “genetically enhanced” first-person, single-player shooter is loaded with some of the greatest, most modifiable weapons to ever blast their way into video games. Explore a living world and take control by hacking devices, commandeering security turrets and crafting unique items critical to your very survival. Make meaningful, mature decisions, that culminate in the grand question: do you exploit the innocent survivors of Rapture or save them?

Other than that, what do you mean about the horror tag being different in context? There’s only one horror tag on steam. People tag the games if they feel like the tag is appropriate. If you want the further context, you come to discussions about it such as this one