the problem is that it is a poorly written law. The mcl is written from the perspective of a traffic stop. If you are stopped while driving your vehicle, and you are carrying a pistol in the vehicle under authority of your cpl, then you would be required to disclose.
In the scenario you present, I would say that you would NOT be required to disclose if you are stopped while walking outside of a store and happen to have a concealed pistol in your vehicle. What if you are walking to the store, and your vehicle is 20 miles away (with a loaded pistol inside) would you still be required to disclose? [rhetorical question]
When in doubt, it is ok to disclose.
If you actually got a ticket for this, I would contact attorney Dean Greanblat (sp?) and not talk about it on the web.