How do they ensure the same looking person is generated each time?

You can generate consistent faces simply by using random non-existent names. Which in turn you can use to train a custom LORA with Dreambooth (needs about 20 images) or use ROOP (a single one can be enough). And of course you can just mix and match it as you please, mix multiple real faces together into a new one, use dedicated face generators like https://thispersondoesnotexist.com/ and so on.

This barely even takes effort anymore, e.g. quick ROOP FaceSwap with the photo from the article, which doesn't look quite the same due to only a single input image, gets better with more, but that's just shows how easy it is to generate a new face, which will than be consistent with itself.

The hard part is getting an interesting pose, expression and haircut into this, as well as sponsored products and stuff. Generating realistic images with AI is pretty easy, but getting variation into them so they don't end up all looking the same can get tricky.

Edit: Five more minutes of effort and it starts to look a little closer.