1 person =/= 1 address, and the gini coefficient is a measure of wealth distribution among people. bitinfocharts doesn't know which addresses are actually owned by a single person. an exchange, however, has the data and resources to suss it out, or at least estimate.

Looking at that kind of statistics can be interesting as long as you understand that any individual is likely to hold their funds over a number of Bitcoin addresses. That is how wallets work. Single addresses with large holdings are mainly cold storage systems, the largest ones are identifiable as exchanges. So those are coins owned by customers.