I don’t know if this will answer your question, but…
When I download the osFirmwareUpdater.zip file, it initally shows as a compressed file or folder (not sure which).
When I double click that, it immediately changes to a normal file, with four contents: two folders, named _MACOSX and osFirmwareUpdater, and two zero-size file named _MACOSX and osFirmwareUpdater, and two zero-size file named. Yes, the same names as the folders.
The osFirmwareUpdater folder contains a folder named windows, which contains a file named osFirmwareUpdater.exe and several other files and folders. Doubleclicking on the osFirmwareUpdater.exe file, it offers options to Extract All or Run. Selecting Extract All, it tells me that the two zero-size files I named above exist, but no other files are generated. Selecting Run has the effect I described before: the .exe file closes immediately.