The tag is "amb_bg". It's not a replacement for describing the background, rather it mostly alters the pallete of the scene to fit a murky FNAF location. This lora was trained on character-free backgrounds from a mix of FNAF 1, 2, 3, SL, and UCN. It was created with Moonbeam.
You may notice that the tag is different than the Anything-v5 and Moonbeam Versions, this is just some nitty-gritty tag behavior stuff. As you may have guessed, "amb_bg" is short for "Ambient Background". (Also as I was setting this lora to train, I forgot the Moonbeam tag.)