FK Issue with Fact Table
I see a tweet as an event happening, so I would model it as a new fact table FactTweet. More specifically as a factless fact.
The dimensions for FactTweet would be DimDate, DimCar (if you can relate a tweet to a car), DimAuthor and I would probably keep URL and Description as degenerated dimensions. You could potentially add the sentiment of the tweet as well (positive, negative or neutral).

DimCar and DimDate would be  conformed dimensions for both FactTweet and FactCarDetail so you would be able to report on both fact in a single query.