This is not what happened. They were granted the rights to sublicense it. Placing a piece of work in public domain automatically grants others to do whatever they want with it including sublicensing it.
Happy now?
The problem isn't that Getty is trying to license an image, the problem is Getty is contacting people already using a public domain image and trying to get them to pay them money to use it.
That's sort of like me selling you a driving license - when you already have one, and I don't actually have any authority to grant or rescind that permission either way. I mean; sure... you will have the permission after the sale, but it's at least a pretty dubious construction.