Also not an expert. I think it only applies if you store the info.

I'd guess number plates may not considered personally identifiable information, or they might be in general but it would be easy enough to hash them to avoid storing this info. You'd still get the info on how often certain plates come up.

Smart screens guessing your emotion wouldn't need to store this info. Once you stopped interacting the info isn't useful and can be discarded.

The ads at Wellington Station with the cameras might just be working out how many people read them.

It really depends on how they are using it the info. It seems most of the time you could have the device get an answer (is this person looking at me? How are they feeling? How often does this vehicle drive past) without having to store personally identifiable information.