One thing I noticed when working with docker and cross platform registries was that sometimes you can pull the same image tag from a remote registry and get different images depending on which platform you requested. It was certainly working in a different way than the local list of images! Digging deeper I learned that it wasn't something new, and it was up for close to half a year now! You can read the official announcement here: https://blog.docker.com/2017/09/docker-official-images-now-multi-platform/
Basically, when you try to pull an image from a repository, your client would actually pull a manifest file listing either the details of the image, or a list of images that can be pulled based on the local machine's cpu architecture, os platform and version! This way you can pull the same image on various machines, and have it running on just about any platform you want. This is especially powerful with the release of Docker for Windows 18.03 where you can run both Windows and Linux images on the same machine side by side!
The manifest format is quite simple, and easy to digest! For example, this is the manifest for my Hello World app that I created to test multi platform docker deployments: