Sam Song Li really did take improv classes at Groundlings to prepare for his role as Bruce Sun.
In Episode 2, when Charles is talking to his mother about the gangsters that have already been killed back in Taipei, he mentions two of their names were Sammo and Hung. Sammo Kam-Bo Hung is a well-known actor, director and producer in Hong Kong cinema. He has also had some fame in the United States. He and Michelle Yeoh have starred in a number of movies together.
The "San Gabriel" universe in which the film takes place is based on real life, but fictionalized in numerous ways for the series. While there's a small city called San Gabriel, the area is principally known as the San Gabriel Valley, a.k.a. "SGV" among locals. Bruce attends California State University-San Gabriel: while the CSU system is real, they don't have a San Gabriel branch. Still, the setting is accurate on whole: the San Gabriel Valley has the largest concentration of both Asian-Americans generally and Chinese-Americans specifically in the U.S., and the majority of the series is set inside of it.
In Episode 2 when Bruce and Charlie are speeding away from the dinosaur-themed birthday party, a henchman dressed as a Tyrannosaurus Rex yells in frustration while a banner behind him that reads in Chinese "The Age of Dinosaurs Dominating the Earth" falls. This is a reference to a similar scene from the original "Jurassic Park" movie involving a roaring Tyrannosaurus Rex and a similar falling banner that read in English "When Dinosaurs Ruled The Earth".
Charles shares his childhood nickname Little Fatty or Xiao Pang with an internet meme in China.