You can say whatever you want but words matter. It is prudent for us to use the same terminology and definitions as Carnival when we are talking about Carnival's products and procedures to avoid confusion.
Again, Carnival blocks Wifi calling which is provisioned by cellular carriers. Whatsapp is not wifi calling and is therefore not blocked. Yes, you can use Whatsapp or Facetime to place audio calls but they are not carrier-provisioned wifi calling calls and you cannot use Whatsapp to call a landline phone number, which is what most people are interested in if they're asking for wifi calling.
There are ways to make calls to landlines over Carnival's wifi - but that is outside of the scope of this discussion I think. No sense in muddying the waters unnecessarily.