Ah! Okay, I was trying to import the uncompressed course materials folder and contents (subfolders, etc.), and getting just a dump of all of the files.
If I right-click > Import the .zip archive, it comes in fine, with the folder structures intact. D'oh!
The instructions for downloading and importing the materials should still be updated to reflect that they are now at the bottom of the TOC, not under the video. (Also, would recommend spelling out or replacing acronyms like "DBC" or "DE" so it's obvious what it is.). Cheers!