Calculation of quantiles

[https://www.codecademy.com/courses/learn-r/lessons/quantiles-r/exercises/quantiles-in-r?action=resume_content_item](the exercise)

How is the following:

dataset <- c(5, 10, -20, 42, -9, 10) ten_percent <- quantile(dataset, 0.10)

ten_percent now holds the value -14.5 .

being calculated?

I thought 10th quantile means the value that 1/10 of the values are below. since there are only 6 values in this dataset, the first value which is -20 is already 1/6 of the values which is more than 1/10, so the 10th quantile would either be -20 itself or the first value above it which is -9, I don’t understand how the average of the two smallest values is relevant?