"You are both the customer and the product" - that's oversimplified as well. You've just put FB, Google, Credit Cards & Whatsapp in the same bucket. That ain't right either.
There's overlap between being a customer & being the product. But the range is so wide that there's no harm in simplifying it by saying FB makes you the product & Whatsapp (pre-acquisition) is the product.
Well, since facebook obviously bought Whatsapp for the userbase, I think it's quite clear that that's exactly what the users were, though in a longer-term strategy.
There's overlap between being a customer & being the product. But the range is so wide that there's no harm in simplifying it by saying FB makes you the product & Whatsapp (pre-acquisition) is the product.