They went through "De Novo" premarket review as their medical device was distinct from any previous devices. This is a higher standard than the normal "510(k)" process. Both tracks involve a lot of evidence, a lot of documents, and a lot of scrutiny from the FDA.
They went through the harder track of FDA approval for medical devices.
I have no idea why you seem to think the primary way for the FDA to approve of new treatments is somehow... not them approving of it?
The wording is really poor. "Pre-market authorization" is their approval process. As in, you don't get to tell anybody that your device has any medical benefit unless we've assessed it.
