I wish I was that clever, but no. It's from a researcher named Ian Walker, coined in a very interesting article. It has its own Wikipedia page: https://en.wikipedia.org/wiki/Motonormativity

Also mainstream articles: https://www.theverge.com/2023/1/31/23579510/car-brain-motornormativity-study-ian-walker

And a video by GCN! https://www.youtube.com/watch?v=-_4GZnGl55c

I'm surprised that by being in the fuck cars community you never heard the term!

To explain it quickly: You know Heteronormativity, the fact that many people are hetero and assume others are too. This is a similar normativity. Many people (depends on where you live yadda yadda) always drive everywhere and never consider a world where cars are not their only/primary way to get around. They will fail to imagine cities where cars are not as important or common, because they associate transport=car. This is harmful, because cars are in fact very inefficient for most tasks and have pretty bad side effects such as taking tons of valuable space in a city or noise or pollution.