I can see some stuff is different in this version of Puppy Linux.
I did make a USB install of imppup64 9.6.1 using StickPup USB stick installer.
USB is fat32 format.
It made the boot menu entry with pmedia=usbflash
Booted OK.
Saved to the USB stick.
I changed the pmedia=usbflash to pmedia=cd.
It tried to boot, but kept looking for a iso9660 formatted partition, which was not there.
So failed to boot with a bunch of errors.
If I burn the iso image to a USB using dd commands.
It formats the USB stick to iso9660 format
So pemedia=cd would work with it.
But it would be a USB with a closed file system. Read only.
So would need to act like booting from a CD/DVD.
The takeaway here is use a Puppy program to do installs to USB sticks.
Now I need to try installing to a USB, using one of the installer programs out there, that are not Puppy Linux programs.
That grub2 boot loader, booting iso's, is looking more and more, the easy way to go.
I will check using Rufus, Unetbootin, USBimager, etc........ running in Windows OS, that most new users would use.