Has anyone been 'forced' (i.e. not asked or informed but rather ambushed) with a shared transfer?

My wife and I just got into the back of the car and a lady jumped in the front seat. We were waiting less than 5 minutes for the car and I didn't really notice her arrival so she must have been waiting a couple of minutes at most. As I mentioned upthread, the car is often just following behind the bus so it is no quicker - privacy is the only tangible benefit and I thought the situation was odd.