If it’s nothing to do with race, then why is a country with four official languages being called “homogeneous”?

Why do people say China is “homogenous” when people speaking Cantonese can’t understand people speaking Mandarin? It’s because those groups of people have been part of a common polity off and on since the Qin dynasty more than 2,000 years ago.

Similarly, Switzerland has been a thing, in various forms, since French and Italian were considered different dialects of vulgar Latin. The groups that speak the four different languages nonetheless share 800+ years of common political and social history.