I would say that the part you quoted suggests it's not generated on the spot.
However,the sentence in the huge font right before the one you quoted could be reasonably interpreted to suggest it's generated on the spot. And as you mention it just looks like a gallery of images that was already generated.
It's still cool, but I'm a bit irked at the misleading framing. Gwern's website showed us amazing text generation from GPT-3, that had all been generated beforehand. We didn't have to be tricked into thinking it was generated on the spot to appreciate it, so I don't see why that's needed here.
The fact that the link says “Try Now” instead of “next image” or something like that is implying that you are using the AI generation when you click the button.
However,the sentence in the huge font right before the one you quoted could be reasonably interpreted to suggest it's generated on the spot. And as you mention it just looks like a gallery of images that was already generated.
It's still cool, but I'm a bit irked at the misleading framing. Gwern's website showed us amazing text generation from GPT-3, that had all been generated beforehand. We didn't have to be tricked into thinking it was generated on the spot to appreciate it, so I don't see why that's needed here.