Yeah so I had this discussion with some people who actually like ordinals and "inscription" was never a term before ordinals. The conversation was being had because of a coindesk article that referred to an op_retrun as an inscription.

We got a quote from this website https://docs.ordinals.com/inscriptions.html

"Inscriptions inscribe sats with arbitrary content, creating bitcoin-native digital artifacts, more commonly known as NFTs."

So if it doesn't create a token or something that can be traded, who's ownership can be transferred from person to person, then it is NOT an inscription. Therefore, Satoshi did not inscribe on-chain. He put arbitrary data on-chain, but to put arbitrary data on-chain does not seem to be the definition of what an inscription is.