Hello, so sorry about the late response. I have been really busy in my real life lately so AskHistorians has unfortunately had to take a back seat. Anyways, this answer doesn't really need to be too long anyways.

This is actually a complex topic, and there have been many lawsuits over the years by Filipinos trying to claim citizenship. However, the truth is that Filipinos were US nationals, but not US citizens. During the first part of the colonial period they were not restricted from immigration to the US like other Asian groups were, and this was because of their status as nationals. A good comparison would be modern day American Samoa. Guam used to also be like this. After 1935, when the Philippines began its path to full independence, the allowance of immigration was rescinded (which makes sense since it was becoming a different country). However, rather unfairly, this change also reclassified Filipinos already in the US as aliens. The Philippine Independence Act was the one that reclassified Filipinos as a class to be excluded like other Asians, in 1935. If you would like more information on the immigration history of Filipinos to the US, I would strongly recommend the book American Workers, Colonial Power: Philippine Seattle and the Transpacific West, 1919-1941 by Dorothy B. Fujita-Rony.