They're not incorrect. Firstly, you're assuming independent probabilities between the students. If it's a single class of 30, for certain skills it might be

They're not incorrect. Firstly, you're assuming independent probabilities between the students. If it's a single class of 30, for certain skills it might be much more likely than pow(0.5, 30) if they were all specifically coached on that particular skill, or if there are selection effects impacting what type of person ends up in that group of 30. Secondly, even if we grant the assumption of independence, the claim doesn't rely on "unlikely values for ... small". There's many small towns with a student body of only 5 or less people, and pow(0.5, 5) isn't that unlikely.