Why do some Mexicans look Asian?

That's because many Mexicans including my sister in law have Indigenous roots.

Those are actually indigenous features you are seeing in them.

High cheek bones. In Peru, they actually elected a Japanese guy to serve as president for ten years because he could pass as ethnic Peruvian. His name was Alberto Fujimori.

There was a huge wave of Asian migration to Mexico in the late 19th century, based on agricultural jobs.  It lasted for several decades.