On paper you’re absolutely correct. AI PC is marketing rubbish out of Wintel. Apple’s doing a direct comparison to that marketing rubbish and just accepting that they’ll probably have to play along with it.
So going by the intended usage of this marketing rubbish, the comparison Apple is making isn’t to GPUs. It’s to Intel’s chips that like Apple’s, integrate, CPU, GPU, and NPU. They just don’t name drop Intel anymore when they don’t have to.
If they literally just said that the iPad's NPU is faster than the NPU of any other computer it'd be fine, I would have no issue with it (though it makes you wonder, maybe that wouldn't have been true? Maybe Qualcomm or Rockchip have SoCs with faster NPUs, so the "fastest of any AI PC" qualifier is necessary to exclude those?)
So going by the intended usage of this marketing rubbish, the comparison Apple is making isn’t to GPUs. It’s to Intel’s chips that like Apple’s, integrate, CPU, GPU, and NPU. They just don’t name drop Intel anymore when they don’t have to.