Crazyates is absolutely correct. Hz means "cycle per second". Calculation of each hash does not define a cycle because multiple hashes are computed in parallel. A "cycle" here could be the time from one calculation to the next; if multiple units are hashing together they increase the hashrate, but they do not magically shorten the cycle.

Example:
We have a device for which each clock cycle takes 1ns. Its clock rate is therefore 1 GHz.
It takes 10 clock cycles to compute a hash. So the hash calculation frequency is 100 MHz.
The device has 1000 cores calculating hashes in parallel. So the hashrate is 100 GH/s.
But there is nothing here working at 100GHz because there is no cycle that takes only 0.01 ns.

The given "counterexamples" for varied uses of Hz all involve actual cycles with period that can be inferred from the stated frequency.

I think I'll adopt this.