That is a low n, but I’m not sure what the alternative is. Surely random anecdotes (n=1) are even less powerful?

The low n is not the only questionable thing about the study. What a big n gives you is diversity of samples and tighter confidence intervals, but it can not correct for methodological limitations. Specifically, they didn't invite any people with sleep issues or who are already sleeping under noise. Therefore the conclusion is a "duh" - if you don't require pink noise to sleep, then don't add it.

I'm not inviting you to draw conclusions from my semi-random (but informed by years of professional thought about why people like different sounds) anecdote.

Random anecdotes might be less biased. For example, no pressure to publish nor sell a product.