That a successful season is not the standard by which Fisher keeps his job. Merely a perception of hope for the future is. As long as Demoff and the Rams believe they can sell 5 years of failure as hope for the future, Fisher is safe. And to your point, that last 5 game standard is itself completely and intentionally ambiguous so that it can be rationalized any way necessary after the fact.
They want to keep Fisher for at least another year, maybe two. That much is clear. Now it's just about finding a way to sell that.