You did, but you aren’t specifying which. “I bought the car” would indicate that you bought a specific one that is jointly understood. In fact, if you had pre

You did, but you aren’t specifying which. “I bought the car” would indicate that you bought a specific one that is jointly understood. In fact, if you had previously talked about a specific car you were thinking about buying, “I bought a car” would be a strong indicator that you bought a different vehicle than what was discussed.