Here they are on Simply K-pop a week later, singing a lot of it live including all the verses and the break and the part of the prechorus that the woman in black sings solo. The group singing on the prechorus and the chant on the chorus remain prerecorded, so this doesn't answer your question as to whether they really sound like that. The answer might be: when the conditions are right and they're not having to dance at the same time, they probably really do sound like that, though maybe a bit thinner.