In my old lab we used to induce them to spawn with lunar lighting cycles. Which is to say, simulating natural lunar cycles, *not* leaving blue lights on all night long. We had them reproducing like clockwork the morning after the full moon (around 8 AM).
Another source of variation is the type of Pocillopora. Hobbyists sometimes claim its about color, but studies on the subject have found that some strains of Pocillopora damicornis do this and others dont (genetics, not color). Pocillopora verrucosa, like the picture you linked, appears to lack this ability.
I'd guess some combination of lighting schedules and types explains the variation in peoples' experiences with Pocillopora reproduction.
What I find most interesting is the variation in stinging. I had several tanks where Pocillopora spawned and literally never saw it win a stinging battle. It lost to Acropora, Zoanthids, and Psammocora. It lost to Hollywood stunner, but everything loses to Hollywood stunner.
Sounds like some people have found Pocillopora with much more powerful stings than I have!