you have to slap non-technical people with a wet mackeral when you're making a subtle point to them
To the vast majority of people, if it looks like a program, it's a program. The two possible responses are (a) Why doesn't it work?, and (b) Look practically finished - when will it be ready? Tomorrow?
I've been in too many situations like people have already described, where you can't get the idea across that IT'S NOT A REAL PROGRAM.
To us, it's a no-brainer that a mock-up is just a pretty face with zero brains behind it. But what metaphor could the non-technical user be given to make this distinction clear?
I suppose if they're literate enough, "Potemkin village" might work.
Maybe a "prop" for the theatrical?
A "Milli-Vanilli" for the middle-aged?