That's a factor, but given the kaleidoscope of ethnicity in most of SE Asia, it's nowhere near that straightforward. People can and do pick up on social class

That's a factor, but given the kaleidoscope of ethnicity in most of SE Asia, it's nowhere near that straightforward. People can and do pick up on social class based on dress, the way you speak, the way you address others etc, just as they do in the US.