Most of the SEA that look closer to Indians are Maritime SEA (Austronesians), which have more South Asian admixture due to intermingling from the Indian Ocean spice trade. Most mainland SEA look "Asian" but with darker skin and larger eyes, except for Northern Vietnamese, who have lighter skin than other SEA and monolids due to historically being in the Sinosphere. The question of who is Asian and who is not is a lot more nuanced and would likely be answered by genetics and phylogeny much better than phenotypes.