I found this service icon and its description at a UK BMW site,
So, it sounds like you might be right about BMW wanting to encourage you to get the fluid changed. It is not a bad idea, as brake fluid tends to pick up water over time which can both damage internal components and, under heavy braking, may lead to brake failure if the water boils causing you to loose hydraulic pressure.
It is also not a "must do today" (or even this week) thing. In the real world there are lots of cars with very old brake fluid.