Access to images in a Paper Document when downloaded with /paper/docs/download

When I download (via the web UI) a doc and save it as Markdown, I get the following:

# Test

## Test markdown exported with images

Hello world

https://d2mxuYYY.cloudfront.net/obscured/path/my_image.png

and it appears that the image can then be loaded unauthenticated (tested in Chrome's Incognito mode).

For the record, this is the behavior that I want: the workflow I'd like to enable is to allow my team to edit a document in Paper, then export it to Markdown and eventually HTML. And it's much easier if Dropbox hosts the images.

However, my question is: is this documented behavior? I wasn't able to find it in the API docs. I'd like to know whether it's likely to change in the future, so I know whether I can depend on this behavior enough to build a process around it.