Half Asian here. At least in my experience, those questions don't tend to come from a place of malice, just a genuine curiosity of ethnic background since they can't figure it out by look.
Sure, there are some racists too. But I've had plenty of ambivalent conversations that start off that way. Beats starting a conversation on weather or other generic topics.
I've gotten "dude, what the fuck are you?!" you before, which I thought was a hilarious way to breach the subject.
I'm tall, had very long (black) hair at the time and had a dark tan. I could pass as part native, black, Hispanic, Asian, pretty much anything.
It was a fair question.