The last "Bro do you even pinball" podcast featured David Theil, a sound designer who did a lot of work for Stern. From the interview I gathered that it was not unusual for the sound designers to have their own sample game to work with. It would not surprise me if this was such a game. I don't know if the sound designer for pinbot (Joh Hey) is still active in the pinball community, but if he is it might be worth reaching out to him with photos and find out if he recognizes the writing on the ROM chips.