The reason why Filipinos are considered separately is because of the history of them being a US territory. As such, they were considered to be different than other Asian/Pacific Islanders.
Even though they are no longer a US territory, this separation in statistics lives on.
Now as for what Filipinos really are.
They are part of the Malay race which basically includes Philippines, Malaysia, and Indonesia. The 3 nations are really one people, except they were colonized by different type of white folks. Therefore, they adopted different ways of romanizing their languages.
As for the Malays and their relations to the Pacific Islanders. The relationship is quite close. As Pacific Islanders originate in large part from the Malay people.
Are the Malays and other East Asians the same? Absolutely not. Completely different stock in term of origin.
Are Malays, East Asians, Pacific Islanders all counted into one single basket statistically? Yes, but excluding the Filipinos for reasons given earlier.
