Generate an Array of All Object Keys with Object.keys()_something is wrong?

In below, I pass the test. Bu I could not understand this part of Object.keys(). I read the instructions. I need return an array. But why is this correct ?

Your code so far

let users = {
  Alan: {
    age: 27,
    online: false
  Jeff: {
    age: 32,
    online: true
  Sarah: {
    age: 48,
    online: false
  Ryan: {
    age: 19,
    online: true

function getArrayOfUsers(obj) {
  // change code below this line
return Object.keys(users);
  // change code above this line


Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36.

Link to the challenge:

To answer this I’ll refer you to MDN: