The article that user links is referring to GrapheneOS (and other OSS software) as not being "free software" - and they (GNU) delves into it more here.
Basically, GNU is saying software shouldn't claim to be free and open source if they contain non free binaries / other non-free blobs.
The nuances between FOSS and OSS can be confusing. GrapheneOS is not claiming to be FOSS.
To be fair, the offer letter mentions he is working from a remote office (and is able to hire an assistant of his choosing). I'm hoping this whole supercommute nonsense isn't daily and instead like.. monthly for some meeting or something.
Who am I kidding though, a $10M signing bonus? He gets up to $250K per year of personal use out of the jet? They'll even reimburse him $50K of legal and advisory fees he incurs having the offer reviewed by his own lawyers. That's where I stopped reading.