It seems there is possibility of this boss spawning in two spots as your friend mention- however, both would be on -2 "Cobra Floor".
1. Most known:
https://tibiamaps.io/map#33325,31125,9:2

2.
https://tibiamaps.io/map#33267,31095,9:2

This is based on following resources:
Regarding 1st place- Videos on https://tibiopedia.pl/monsters/The_Voice_of_Ruin; https://www.youtube.com/watch?v=fjiKU9Hme-0
Regarding 2 place- Screenshot: https://www.facebook.com/tibiabossescom/photos/a.710989992376885/1842475399228333/?type=3&theater
Looking at Vunira's and Wintera's killing history for this boss, there is a chance that both bosses can appear (or they are always appearing) on the same day- however players either do not realise they killed the boss, or do not check for second spot as unaware there is another one. There is also possibility that the spawning of the boss is triggered by killing mobs in the cave.
Vunira's killing stats: https://guildstats.eu/bosses?world=Vunira&monsterName=The+Voice+Of+Ruin&rook=0
Wintera's killing stats: https://guildstats.eu/bosses?world=Wintera&monsterName=The+Voice+Of+Ruin&rook=0