I am still waiting for someone to explain me why you can forward medias (image or videos) in whatsapp to new recipients without uploading it again completely if

I am still waiting for someone to explain me why you can forward medias (image or videos) in whatsapp to new recipients without uploading it again completely if those images and videos are encrypted with the public keys of your recipients. Since the forward is instantaneous and not involve a reupload, it looks to me the files are cached on the servers. If the recipient can see thee files and they are encrypted, it means that the server itself encrypted it using their public cryptographic key. If the server can do that, it means it either: - can decrypt your own files - cache them unencrypted Correct me if I am wrong. It is easy to test by sending a large video recording over a crappy connection, then forwarding it to another recipient. First upload can literally take a minute or more, the second action is immediate.