Author here. I've been running Windows since 3.0 and I copy my old tool folders with me whenever I change machines or upgrade the OS. This GZIP.EXE is the oldest EXE I have in my \ntbin tool folder that still works. The folder has 579 EXE files.
I think that is the point being made. This exe is cherry picked as the oldest working exe, it isn't like every 30 year old exe in that folder still works.