Yeah it's living and breathing world. NPCs might fight eachothers (different factions) and fight mobs that they find on their journeys etc.
Was it Museum of Technology that was full of ghouls? Or Lincoln Museum or something like that, anyway it was so scary place when I played FO3 first time. Hearing those small foot steps slapping in the dark halls and occasional growls. If you put 1 bullet into ghoul whole museum woke up and ghould poured from every direction, I screamed like little girl everytime (I am little bit bad with scary things).