The number needed for a study to get significant results depends on the strength of the effect it is measuring.
For example if I have a bag full of thousands of coins, pull out 19 at random and flip them sequentially, and they all come out heads I'm going to conclude I have a bag that is overwhelmingly coins that are heavily biased toward coming up heads.
Are you going to say my sample size was too small to support that conclusion?
To see if their sample size was too small you need to at least read the part where they do the math.
For example if I have a bag full of thousands of coins, pull out 19 at random and flip them sequentially, and they all come out heads I'm going to conclude I have a bag that is overwhelmingly coins that are heavily biased toward coming up heads.
Are you going to say my sample size was too small to support that conclusion?
To see if their sample size was too small you need to at least read the part where they do the math.