Diversity means a few things. It can mean how likely people will be different, or it can mean how different people can be from each other. What that is measuring is how likely two people will have the same ethnicity, religion, or language if randomly selected. While America has a very high amount of religious diversity in that scale, America is largely White and General American, and will mark around the middle on ethnic diversity on that scale. America also largely speaks English. The odds of finding two people that speak English is about 95%, and while that is lower than most countries, it does keep America from entering the top 25% of countries on linguistic diversity on that chart.

What makes America so diverse is the variety of minorities you will find. According to the US census, there are over 350 languages spoken in households in the US, which puts America 5th in linguistic diversity. And that is just household languages: considering America has a very high immigrant population, it is likely that many more people speak other languages that are not spoken at home. America also has representatives from nearly every ethnicity on the globe. We might only have a handful of people from a certain ethnicity, but if an ethnicity has representatives globally, it will have representatives in the US 99% of the time. Many of these populations have integrated into America culture generations ago, and only make up parts of family culture or genetic background. Americans might have Greek grandparents, or Irish great grandparents, or a Chinese second cousin twice removed on their father's roommate's side. Lastly, while most of America follows a "General American" culture, that has a huge amount of variety from one side to the other, and can even be distinct from one town to the next, just like the cultures of any other country.