Ouch. As a Vietnamese female, I can say I don't mind if people mix me up with other races. Heck, if I'm in another Asian country and they start speaking to me in the native language, I won't even be offended. But no matter what race you are, what you experienced is disrespectful as fuck. You do not go anywhere in any professional setting and speak to someone like that. You shouldn't even do that as a tourist unless you're in a brothel and have already paid!