It's not completely clear but I found these public access instructions below.
Create a shared link if you want anyone to be able to click a link to access your file—people don't need a Dropbox account to view your file.
People can:
view files
comment on files
download a copy of files
But, people can't edit the original files in your Dropbox.
To share a link
If you haven't already, install the Dropbox desktop app on your computer.
Right-click the file and hover over More…
Choose Copy Dropbox link.
The link will be copied to your clipboard. You can then paste it to an email, message, or wherever people can access it.
https://www.dropbox.com/help/167