So, I already downloaded the Mac version. I launched the game & was presented with a Play button. I pressed that & it started to download something.
So, I tried to find out what it was downloading. I went to "Library/Application Support/Telltale Games/" and found a "BackToTheFuture101 DRM 15.05" folder. To my surprise, it was downloading "bttf_101_setup.app.zip" again. It seems a bit redundant, don't you think?
Any other Mac users having the same problem?