It's a reference to measures of intelligence sometimes being poorly thought out. Imagine if a monkey society came up with a basic competencies list. Among the list would probably be the ability to climb a tree. Now imagine if the monkey society tested a fish according to their competencies list. The fishwould be deemed lacking due to their inability to climb a tree.

It's the same thing with asking a painter to measure the stars or asking a manager to do middle school-level math.

It's a figure of speech