No need to get jumpy here…
The vocals are from a few very rare sample CD’s with vocals of original indian and african singers. Those singers have learned to sing from very early age on, having learned it from their families and other professional vocalists. Many of them never heard about auto-tune etc.
On thee other hand I can imagine that Ott retuned the whole samples here and there, when it had to fit to other instruments. So it is both, perfect vocals and artistic freedom.