The supported way to transfer files to ArbOS is by initiating the transfer FROM ArbOS. (You technically can SCP to the shell of an ArbOS device - it's not supported/recommended)
Notice that the absolute path is used to reference the file even though it's in the home directory of the user being used to login to the remote machine.
system files copy scp://ross@<my-local-machine>/home/ross/arbos-7.3-NGEN-x86_64 disk