It’s not you, it’s SVNSVN Short for “SubVersioN”, it’s the code management system used to maintain the plugins hosted on WordPress.org. It’s similar to git.. And you.
The tl;dr is that the MIME Types on your images aren’t correct. Per Otto:
On Windows, using TortoiseSVN, you can right click the screenshot file, and select the TortoiseSVN->Properties menu. There you will find the svn:mime-type property, probably incorrectly set to “application/octet-stream”. Change that to the proper mime type of “image/png” or “image/jpg” accordingly. Afterwards, commit the change.
If you prefer command line SVN:
svn propset svn:mime-type image/png screenshot-1.png svn commitOr similar. If somebody uses a different SVN client, look for “properties” and then the svn:mime-type property.
Once you do that, upload the changes and go make coffee. The information will sync out, but it may take a little while.