In this particular case, running into someone you haven't seen for a while, that question is so illogical that you shouldn't give it a moment's thought. That person knows nothing about your situation. You might live right around the corner from the grocery store, you might rent a garage a short distance away, it might be actually farther to walk to your car, drive it two blocks to the store, load it up, drive two blocks to the garage, unload the groceries, and carry them two blocks to your home which is one block from the store.
Of course that's not your situation, but that's not the point. There could be half a dozen reasons why you are at the grocery store on a bike and you still might own two automobiles. I would just laugh off that one. "Your car smashed up?" "Haha. No. So what have you been up to all these years?"