Carrying in a vehicle is not Open Carry, it is Concealed Carry per state law. It is covered by more out-of-state licenses than regular Concealed Carry, but it is definitely not Open Carry as such. I stand by my statement.
The problem with that is that most people don't understand this difference.
You tell them OC is legal and they have no idea that vehicle carry is considered concealed. My point is only that I usually reply similarly as you did but with the added info about the vehicles.