None of what you're asking about is relevant. The only material fact is that Set uses the equals() method to determine object equality, and that's in the Javadoc. HashSet and rehashing and 'how it uses memory to store HashSet object' have exactly nothing to do with it.
and would be implementation dependent per JVM. I seriously doubt any competent interviewer would ask that as a question, far more likely OP misunderstood what he was being asked.