That is what the NEC says to use for the circuit to the motor. They probably said 16 ".5" so you wouldn't use 14 ga wire and a 40a brealer
That is usually a question on the inspector test. FLA=16 with internal O/L protection, what is the min wire size & max breaker. Answer #14cu, 40a. Now days breakers are usually HACR so you don't need one that big to handle the locked rotor on start up but the code hasn't changed.
The 14ga = 15a, 12ga = 20a 10ga = 30a we all know is really 240.4(D) and is aimed at the circuits that are likely to have receptacles, where the installer has no control over what gets plugged in so the
80% safety factor is built into the breaker size limit. Folks will keep plugging things in till the breaker trips, then unplug the clock if that will let it hold.