Re: Being a U.S, government contractor
I suspect the US government in the form of one or more of its security services is already privy to much of FB's WhatsApp traffic and that it has been for some time with FB complying via their legal obligations. So NSO was likely operating for another actor such as the Saudis or even Israel, I am sure there are many outside the US who are interested in certain data within the US, so it could be anybody.
NSO say they only provide their services to governments but considering the nature of the services they offer I doubt thier moral compass and veracity.