For one it uses a numbers of sensors: https://support.apple.com/en-us/HT208108 But also to generalize to makeup and occlusion and millions of faces you have to do much more. There are hundreds of papers on the subject.

Face ID sensor will projects 30000 infrared dots onto the user's face, and then it reads the projected pattern. The pattern is sent to a deep neural network in order to confirm a match with the phone owner's face.

The technique in the article does not seem to be using depth data (there is a picture in the article), only RGB image data.

So, he could have gotten the same results with a webcam.

My understanding is that these depth cameras create a 3d point cloud and use the rgb to map/overlay color onto the 3d.