It would possibly work with XLSX or PPTX or any of the newer Office file formats that rely on zipping a folder of XML files. Open Document Format files like those from Libre Office might be capable of this too.

XLS, PPT, DOC or other old style Office files don't follow this format so this specific approach wouldn't work on those.

I would say it is because it appeared that in the end he relied on renaming a filename in the zip to a script tag with contents.