I'll try to figure out how to readd that: I did notice that in my playtests of the mod pack they sometimes spoke a few things (typically negative) and occassionally played on the guitar, but most of the time they did stay silent. Very sad.
I think Call of Pripyat removed that due to a larger focus on one big safe location (Skadovsk, Yanov station, Laundromat...) instead of a bunch of camps around the general locations, and in Call of Chernobyl it's just a leftover. Doubt I can actually figure out how to recreate that (I am a bit amateurish after all)... Or can I?
While digging around CoC commits on bitbucket, I found a camp.ltx file. This file is missing from my 1.4.22 unpack; I'll keep looking and see if I can find out which file references it, because the contents of this file are interesting to say the least:
[camp]

stories = s_story_1, s_story_2, s_story_3, s_story_4, s_story_5, s_story_6, s_story_7, s_story_8, s_story_9, s_story_10, s_story_11, test_story

guitar_themes = test_guitar

harmonica_themes = test_harmonica