As I understand it the majority of Sushi restaurants in the US (dunno about China) are run by Koreans. There was a weird religious cult thing that did the legwork to set up sushi grade fish distribution on a large scale and flooded the market with restaurants.

Sometimes the clues are really blatant that it's not an authentic Japanese restaurant. There used to be a Sushi place a few miles down the road where the hirigana on the sign spelled out Arikato.