What I think is more likely is that parents are more likely to name their children with some names based on their ethnic background and it's easier to guess ethnic origin in adults than in children.

If you have a stereotype of what an ethnic group, say Ashkenazi Jews or Greeks look like, and Jews are more likely to name their children something like Daniel and Greeks are more likely to call their children Theo, then if you give people a picture of a Greek guy and ask if he's an Evan, a Theo or a Daniel, they'll subconsciously stereotype and say Theo.