Let me try to restate things simply and clearly as possible.

Encapsulation is meant to keep private instance variables private, i.e. mutations should not happen without the class allowing it and being aware of when it happens.

If an object via Dependency Injection passes an object by reference to a constructor and that constructor puts the passed object into a private variable, the calling function can break Encapsulation since it still holds a reference to that object.

This means that the calling function can mutate the now “private” object without the permission of the container class and therefore without its knowledge.

I hope this makes sense.