Java List doesn't contain Bytes

Question

I really can't explain this one. I have a Java List<Byte> myList; that is set like this:

class AJavaClass {
    // ...
    private List<Byte> myList;
    public AJavaClass(List<Byte> myList) { this.myList = myList; }
    // ...
}
AJavaClass aJavaClass = new AJavaClass(customMongoRepository.customFind());

The customMongoRepository object is injected via Spring. It is defined like this:

public interface CustomMongoRepository extends MongoRepository<AComplexClass, String> {
    List<Byte> customFind();
}

However, when looking inside aJavaClass during execution, myList is actually of type List<AComplexClass>.

Now, what I understand is that the query executed in customFind doesn't yield a List<Byte>, but rather a List<AComplexClass>. What I don't understand is how this doesn't throw an exception, and how a variable can contain a value of a different type.