Agreed. I'm mixed race as well, my mom was white, my dad was Black. I look very white. I've enjoyed privilege as a result, sure. People assume I'm white when they see me. I've never had to make people beleive it, they have fucking eyes, they beleive what they see. Their tune and treatment of me often changes with they find out differently.
So she described herself as white on a form. What were the options? I've encountered many a form with a dropdown menu that doesn't have a mixed option. Looking like me, what the hell else am I going to pick? Can't pick Black because when my white self shows up, well, I'm a liar, right? But I can't pick white either, because, what still liar? So you go with the option that best fits. It doesn't make a person untruthful.
The author here doesn't grasp the confusion and delicate straddling of 2 worlds, neither of which fully fit, we walk in. She doesn't understand the acceptance and approval that can be snatched away in an instant based simply on a tiny piece of information coming to light.