I believe it’s removed because the file is too large. By default, the max image size kb is 4096kb, and this specific file is > 5000 kb.
From my understanding, if you upload an image, it’s automatically resized/compressed before sending. You can upload large photos because of the client-side browser optimization.
With download remote images to local setting, Discourse will try to download the image as it is, and if it’s too large, it will be removed from post content.