Correct me if I'm wrong:

The org chart is built based upon the "manager" attribute, yes?

The "ismanager" attribute is used when you're doing a Manager lookup
(ie, if the person is not a manager, you can't find them).

What is directreports used for?

In our case, I think manager and directreports would be one and the same
(ie, the person we report to is our "manager")

Did they include it just in case they're different?