Hi Erty,
First, let me say "welcome to the website" to you.
As far as I am concered, 'a compound noun" is a noun phrase of which at least two nouns are combined together and function as a noun. Usually, in our language, we will have a different translation of "car factory" but we need to interpret it backwards to understand it fully. Between the two nouns "car & factory", the key noun is the second one "factory" and "car" is just used to show what kind of products the factory makes.
Just some ideas.
