They aren't in debt. They sold something like one seventh of their company. That's not enough to lose control of the company in any meaningful sense.
You're correct that they haven't lost control, but now they have somebody to answer to. Somebody who just gave them $100m. Somebody with more equity than all but a few of the people involved. Somebody who's powerful and respected and whose job is to push tech companies in the direction of maximum return.
It changes things.