Why in one case destructuring assigment returns a values of objects and in other case objects

I'm setting up test for my nodejs-cli app, and there's two tests, when I invoke function, which returns a object and do a destructuring assignment in one case it works properly in other in returns a object.

describe('a credential manager', () => {
    var creds
    before(() => {
        creds = new CredentialManger('twitup-test')
    })
    context('with no existing credentials', () => {
        it('should prompt the user', async () => {
            sinon.stub(inquirer, 'prompt').resolves({key: 'foo', secret: 'bar', accessSecret: 'shot', accessToken: 'batch'})
            let [key, secret, accessSecret, accessToken] = await creds.getKeyAndSecret() // HERE IT IS
            expect(key).to.equal('foo')
            expect(secret).to.equal('bar')
            expect(accessSecret).to.equal('shot')
            expect(accessToken).to.equal('batch')
            expect(inquirer.prompt.calledOnce).to.be.true
            inquirer.prompt.restore()
        })
    })
    context('with existing credentials', () => {
        it('should just return them', async () => {
            let [key, secret, accessSecret, accessToken] = await creds.getKeyAndSecret() // AND THERE IS NOT
            expect(key).to.equal('foo')
            expect(secret).to.equal('bar')
            expect(accessSecret).to.equal('shot')
            expect(accessToken).to.equal('batch')
        })
    })

Output

 a credential manager
    with no existing credentials
      ✓ should prompt the user (61ms)
    with existing credentials
      1) should just return them


  1 passing (271ms)
  1 failing

  1) a credential manager
       with existing credentials
         should just return them:
     AssertionError: expected { Object (key, secret, ...) } to equal 'foo'
      at Context.<anonymous> (test/credential-manager.js:27:28)

It is works fine then I destructure an array of one object in second context

let [{key, secret, accessSecret, accessToken}] = await creds.getKeyAndSecret()

Why this is happening? What the difference between those calls?