FWIW the notion of unscrupulous food vendors serving dog/cat meat is pretty common in other cultures, and it doesn't exclusively apply to Chinese restaurants. I've heard it in just about any context where meat is served.
To give a specific example, there's an old Soviet joke about a guy buying meat pierogi from a street vendor; after closely inspecting them, he asks: "So, did this meat bark or meow?", to which the seller replies, "Neither; it asked too many questions."
To give a specific example, there's an old Soviet joke about a guy buying meat pierogi from a street vendor; after closely inspecting them, he asks: "So, did this meat bark or meow?", to which the seller replies, "Neither; it asked too many questions."