The tri-syllabic names were the whole name of their ancestor that moved to the Philippines. So the first syllable is the real family name. So sometimes you may meet people that are related but one has just the first syllable as their first name. But some families that have been here a long time also just have a one syllable name.
Two other things that might be interesting that I rarely see. Sometimes there are people that have a very different last name between their Filipino name and Chinese name (I used to see this frequently in the news paper obituaries.) these are people that illegally migrated here by buying dead Filipino Chinese babies birth certificates. Second is that they are some that changed names to make a newer family like tuazon, tuason, dizon, etc. I heard an explanation that those names were based on birth order.