In general, any time you save a photo on iOS, it goes into the camera roll, which is automatically backed up into iCloud.

That wasn’t the claim though, the claim was that if I text someone a photo via WhatsApp it will do all of this automatically without them choosing to save it.

If WhatsApp does this by default then, ho boy is that a terrible implementation.

Try it? I'm not Wikipedia, first party research is allowed. Go for it