You're correct, he's wrong. How do you explain pearling on plants when the lights are on? That's oxygen being formed during the day. BTW, it's the oxygen level in the tank that leads to higher coral growth, not the PH, which tends to be correlated with O2. I'll reference the scientific literature here shortly.
Pearling is produced in planted tanks when the tank water can no longer keep the O2 being generated by the plants in solution, so it forms bubbles.
Oxygen dissolved in the water (or undissolved when pearling) has no effect on pH.
CO2 dissolved in the tank is what causes pH to drop by generating carbonic acid.
Here's some scientific literature: