Java's private access modifier means only private for a class, as you correctly pointed out. This ways any instance of this class can access the private members of another instance of this class like they were public. That means you can directly reference the fields or methods of a Car instance if you are inside another instance of Car. This is often used in implementations of the equals() method for example.
This example is not the best but it shows that you can directly access private members of the other Car instance
I guess this concept of "private" access is confusing for a lot of people who are new to Java. At least it is not obvious at first sight that members can be accessed from different instances even though they are private.
On the other hand it would be very difficult to impossible to implement something like the said equals() methods. Without the private access modifier working the way it does you'd have to expose more internal data than necessary via getters or other methods which in general is surely not what you want.
Anyway,! I'm glad that my answer helped to clear your doubts.
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