I have friends who are 1/2 1/2 and who look more asian, and others who look more white. I have 2 1/2 1/2 friends who have a kid - they both look more Caucasian and their kid looks more Asian. I think men are kinds of stuck with what they get, while women can use hair/makeup to move the line a little.
Serge, I don't think that is the answer to his question. He is not asking why some EAN may look more Asian, or more white. I think he is asking why some people may think that the very same EAN looks white to some people, Asian to others, and mixed to even others.
EANRABBIT, if you travelled around a bit, you might even find more combinations. I got that white sometimes, Asian sometimes, mixed other times, and people say I change from day to day and throughout my life. If you were in the USA, there may be some who think you are Latino or Native American too. In China, some might think Uighur, or other Central Asian. In Hawaii, some might just think you are some ethnically ambiguous local and classify you as Haole or non-Haole depending on how you think or act. Or if you speak with a British accent, then as some NON-local who is, well, simply British.
So I think people see different things, pick up on different cues, etc. etc. based on their own personal background, how YOU act (eg, if you switch from a European to an Asian language) and maybe just how they feel that day. What is more important is that you take a stand on your own identity. You can define it for yourself, and not have to simply let people define it for you. Read Maria Root's "Bill of Rights for Mixed Race People".