Yes, people from India are classified as Asian-Indians to differentiate the term from Ameri-Indians (Native-Americans).
I’ve seen that classification & terminology over the past few years.
It is true that they are not a monolithic voting group, but because the Vietnamese, Filipino, Samoan, Viet Cong, Laotian, and other groups represent small fractions of a percentage, they generally end up lumped together.
Your examples above perfectly illustrate the problem.
The Vietnamese, Khmer, Malay, Thai, and others in the SE Asian region are not of the same ethnicity.
So if one wants to conduct political opinion polls based on the East or Southeast Asia geographical region, that's one thing.
If one then says "Well, it's really a poll of the Asian ethnicity," it is absolutely stupid.
There is no "Asian ethnicity."