FAANG companies need specialists not generalists. Being large companies, they have groups of people to work on dedicated aspects and technologies. Employees can have a very narrow and specialized focus.
You're both correct! A company like Google hires both generic SWEs, who are hired without a specific project in mind, and super specialized roles like (say) wearable hardware integration engineer, who are hired to fill a very specific niche.
The product they're working on might be super specialized, but oftentimes the skills needed to do the work might not be.