You'd have to have a massive leak on the valve guide to get zero differential pressure...and at that you'd have a hard time loosing the pressure if the valve was closed...air doesn't leak past the valve guide when the valve is closed you see. Not if the valve is seated properly. When air does leak past the valve, it goes out the induction or the exhaust. If it were to be leaking past the valve guides, you'd have to have a sealed induction and exhaust to know it, and a very leaky valve cover gasket.
What this means is that the test was very improperly done. If you've got valve guides so badly shot that the compression is zero, even if the compression test could show that, you'd have fould plugs right away, considerable oil loss, and smoking cylinders.
The valve guide seals weren't leaking. Perhaps your valve guides were bad and not allowing the valves to seat properly, or to seat inconsistantly. Again, here the actual pressure doesn't tell you anything. Listening at the exhaust allows you to hear a hiss of air; you know to start looking at the exhaust valves. A hiss of air in the induction lets you know to start looking at the intake valves. A hiss of air from the engine breather or through the dipstick/oil filler tube indicates blow-by on the rings.