I also agree with Red. Assuming it was something that they would have had to remove the brakes for the mechanic could have just been on autopilot re-installing them, etc. I'd certainly ask them about it, have them fix it, and be sure to be clear that you want them "backwards" in the future.

If they had no reason to remove the brakes then I certainly agree they most definitely should have consulted with you before taking the initiative to "fix" it. How they responded when I brought it back in would determine whether or not they ever touched my bike again at that point.