This is just showing we don't need to adjust the valves clearance on a regular basis because their are maintenance free. It's not telling me if my engine is an "interference engine" or a "free-running engine". See excerpt from a technical repair manual :
If the timing belt breaks on an “interference engine”, mechanical engine damage will occur. Most commonly, the damage involves the pistons hitting open valves, resulting in the need for expensive repairs. In extreme cases, replacing the engine may be required.
Breakage is not the only reason to replace your timing belt. Looseness and wear can allow the timing belt to slip, resulting in very poor performance, a no-start condition, or engine damage.

The valve clearance is at the top of the valve rod between the valve and the camshaft. What I am looking for is the distance between one fully open valve and the top of the piston when at max high position. If this distance is negative or even zero, the valve will hit the piston and damage will occur when the timing belt breaks.