False.
Numerical proverbs are not found only in Ecclesiastes, but are also present in other books of the Old Testament, such as Proverbs and Psalms. For example, Proverbs 6:16-19 lists "six things the Lord hates, seven that are detestable to him." This style of using numbers for rhetorical effect is known as numerical parallelism, and it is a common feature in Hebrew poetry and wisdom literature.