Yeah, it's their short hand for the way for describing the phenomenon of how car culture impacts what we view as "normal".

For a while advocates use the term "windshield perspective" to describe how from behind the windshield you have little understanding or empathy for the way those outside a car may need to use the street.

Some researchers are using the term "motornormativity" to describe the phenomenon of that leads many americans (or in this sudy I believe brits) to think it's not ok to leave your private property on the street, but it is ok to leave your private vehicle on the street, or it's not ok to have kids breathe your second hand smoke, but it's ok to have them breathe your car exhaust.

Once you have a culture that is so use to automobiles, it becomes hard to convince people to walk even 500 meters to the store, whereas in the past you would walk maybe 3-4km and it would not be noteworthy.

Motornormativity also causes us to pave over (pun intended) the sheer financial burden of vehicles (second largest household expense outside of housing), the deaths associated with them (a leading cause of death for those aged 1-49, 40k/year in the US), and the environmental impact -- both pollution and inefficient land use.

So yeah, carbrain is a silly term to describe a very real phenomenon. Another way to think about it, if you described the way we use cars, the death they inflict, the environmental damages they cause, the lack of physical exercise they encourage, extreme dedication of space, etc to your great-great-grand parent, they would think you are crazy, but you think it's normal.