From Faith Futures
The commentary in [The Five Gospels] (p. 298) reads:
The difference between a proverb and an aphorism is not always easy to discern. This saying has the sound of a proverb, yet it also has an edge to it, particularly if spoken, let us imagine, with reference to Judean officials or in the context of discussions with church authorities or academic philosophers, to cite only a few possibilities. The weighted average fell into the gray category because the Fellows could not decide whether the proverbial character of this saying identified it as common wisdom or whether its potential edge identified it as an aphorism spoken by Jesus.