Isn't the concern with over the air updates and back-doors? As in, if the citizens in county A buy country B's cars, and now there is a tiff between the two countries, country B could potentially brick all of those vehicles in country A.

That is just another variation of geopolitical worry. Nobody will do this unless there is a geopolitical situation happening. If you are going to war then bricking the enemies cars is useful. Otherwise it is harmful (even if you do it accidentally you lose trust and so nobody will buy from you again - which is why so often rollouts are done slowly - if it doesn't work you only have a few customers affects and can spend more than a car's value on techs to fix them thus ensuring you don't lost reputation)