I use Mac's steam version as well. I'm not sure how well RFC: DOC will work on mac, because mods with custom DLLs don't work on Mac.
I'd suggest downloading a software, such as Keka, that can open 7zip/rar files, then depositing the extracted files in /Library/Application Support/SteamLibrary/steamapps/common/Sid Meier's Civilization IV Beyond the Sword/Beyond the Sword/Mods
or a similar directory. Then, load up the game and load mods like you normally would.
(If you don't know how to access the library, go to finder and hit the "help" tab on the very top of your screen (outside of any window). Then type "Library" and click the result with the same name. Navigate further until you find the last file in that string of code.
If it works, great! I'd like to play it with a friend of mine but I'm not sure how compatible it is.
If not, try looking around the CivFanatics forum for mods that don't use custom DLLs or are explicitly mac compatible. For instance, History Rewritten changes lots of aspects of the game and attempts to make them historically accurate, but doesn't have the timing of events or historical starts that RFC or its modmods has.
That's pretty unusual, but wouldn't be the first time that Windows got such information wrong.
You can take another look at the issue with a program like WinDirStat (alternatively, download it via Ninite).
If this happened to me, I'd be curious, but I wouldn't be worried.