This study is tiny and of negligible value. They didn't even try to pretend it's of real value, and instead just dropped the classic "our study clearly demonstrates that people should probably study this stuff". Conditioned norms are by far the most relevant condition for sleep for most people, and sleep studies of tiny durations with tiny sets are basically just noise makers (har har). Even worse, they seem to have specifically excluded people who already use noise machines, ensuring that their participants were conditioned for the silent norm.

Scientific method, statistical rigour...eh, this looks like a headline chasing study.