When you reduce human beings to characteristics, often stereotypical of their race, ethnicity, or culture, you are objectifying them to fulfil your own personal wishes and expectations for how they should look and/or behave.
Treating it as something distinct from racism tends to hide the realities of the situation. Social norms, representations and power relations all influence our tastes. Including our sexual preferences. What we find beautiful is not natural. Ever-changing standards distort our perception of beauty. Those are far from being neutral from a racial perspective. People are not born with racially-specific sexual preferences. We are not even born with an awareness of race. So let us not pretend these are random occurrences, with no causes, no reasonable explanations, no culprits. Your tastes can be racist, too.