The original Reddit post on the subject.

A screen grab of the original police report.

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It just shows how much the world sees Eurasian men as Asian. This wasn’t based on anyone knowing that Elliot Rodger was mixed race and had an Asian mom. Just by looking at him, in the chaotic situation of his shooting spree, he was identified as an Asian male. And Elliot was a legitimately mixed-looking Hapa. He was proud of it. Shortly before his killings, he was linked one of the Eurasian blogs in a bodybuilding thread and he replied “I thank god everyday I don’t look Asian at all”. Elliot Rodger put down full Asian men as disgusting and repulsive to women. 

So it just shows that even Hapas who don’t think they look Asian, are identified as Asian male by others.

http://www.sbsheriff.us/documents/ISLAVISTAINVESTIGATIVESUMMARY.pdf

The police even arrested one of Elliot Rodger’s Asian male victims, who Elliot hit with his car, since he had the same race as Elliot.

At the end of the pursuit, Keith Cheung was handcuffed because deputies thought he was possibly a second suspect. Cheung matched one of the suspect descriptions that was previously provided (Asian male, white T-shirt). Cheung’s proximity to the rear passenger side of the suspect’s vehicle led responding deputies to believe that he was involved. It was quickly determined that Cheung was a victim who was riding his bicycle when he was intentionally struck by the suspect’s vehicle. He was provided with medical attention and released from handcuffs.

http://www.sbsheriff.us/documents/ISLAVISTAINVESTIGATIVESUMMARY.pdf