It's pretty darned good except for a couple of details. Take a look at a steam locomotive. At zero RPM the cylinders and wheels are dead stopped, but the cylinders are still capable of exerting enormous torque, enough to move an entire train from a dead stop.
The dynos most people get on (dynamic acceleration dynos) measure torque (how fast a drum of a given mass accelerates as the engine speeds up) and uses those two numbers (instantaneous torque and RPM) to calculate horsepower. Torque and horsepower are related directly. There are dynos that measure horsepower directly. One type measures how much pumping ability the engine has when connected to (typically) a water pump of known efficiency. You measure the flow rate and the differential pressure across the pump and you know the horsepower. Using those numbers and the RPM you can calculate torque.
You can use either number to develop an engine. Torque (and gearing) tells you how hard the vehicle will accelerate. Horsepower is the measure of power production, torque over time if you will.
The rest of the article is more clear and well-presented.