What is the meaning of the term "Ground Paddle" in the context of ORG1411 PCB design?
The wording and the illustration clearly show copper on the top layer, masked with solder resist. It's required to be connected to the main ground plane with multiple vias, whichever layer that ground happens to be on.

Those multiple vias would be passing through the volume that fig 19.3 shows as copper keep out. It's potentially ambiguous, as vias are copper, but I'm sure it means copper tracks, as too many tracks would impede the placing of 'multiple vias'.

It's a pity that they use 'must' and 'should' in successive phrases below 19.1, as usually 'should' is weaker than 'must', but it still means 'do it unless you really understand why you're not'.