I did not read the results, but this definitely depends on the effect size and the variance of whatever they are studying. If 31 people were raised from the dead, for example, it's plenty of sample size.
The issue is that the sample might be highly biased. If it's just 31 white males from Lubbock Texas then what does it even say? Stoners in that town speak different?
With such a small sample size, formal methods break down. The sample could be biased. In fact, it's almost guaranteed. The ability to p-hack (even inadvertently) is extremely high. Publication bias is also practically guaranteed. These kinds of issues void significance to a reasonably high degree.
At these kinds of sample sizes, the biggest issues are not going to be included or visible in the study. Unless the reported significance is extremely high, it's not meaningful.
