The recommended yarn was used in a featured project, and is just one of many choices you can make for your own project. Pattern calls for worsted weight yarn, but was written before aran was a commonly used term in the US for yarn weights. The gauge listed is for an aran weight yarn.

from the pattern:

This hat fits and flatters everyone from little kids to grownups. Knit one in an evening of TV watching or a week’s worth of coffee breaks. Good idea for someone whose size is uncertain or for charity knitting. The stitch pattern is baby cable, also known as mock cable.

Pattern has a choice of right or left twist cables.