“Steganography goes way beyond .zip files.”
Sure, but the false claim that is being made about this specific file is that there is a zip file hidden there. There is no zip file. Short of finding the first two letters of a PKZIP header, there is no evidence or claims of anything else hidden there.
I understand your point. I’m giving this credence, because I’ve been following what the 4chan guys are doing on this closely, to the extent I can. (They’re doing most of their work off the visible boards like 4chan and reddit. Places I’m aware of but won’t mention or visit. They’re not places for old folks like me.) I’m inclined to believe they’re on to something.