DownCasting Failing In Custom APEX Classes

Readme.md

This is related to the question posted on SalesforceSE: https://salesforce.stackexchange.com/questions/226922/downcasting-failing-in-custom-apex-classes

I got curious with one of the answer suggested and wanted to try so updated Term_Segment__c refence to Contact object.

When I am trying this code, it shows error on line numbers 12,13, & 14 in ContactObject class.

Please see this video:

Update:

Was able to get rid of the above errors by downcasting to Contact object but it still shows error when downcasting object of instance SubscribeObject to ContactObject.

Please refer to this video: https://vimeo.com/282194861

ContactObject.cls

public class ContactObject extends SubscribeObject {
    //Instance
    public Contact record;
    public Contact oldRecord;
    public Contact originalRecord;    

    public ContactObject(SObject record, SObject oldRecord, Boolean editInPlace) {
        // super needs to be the first thing called, if you use it
        super(record, oldRecord, editInPlace);

        // the accessor methods are inherited, and visible
        this.record = (Contact)this.getRecord(); 
        this.oldRecord = (Contact)this.getOldRecord();
        this.originalRecord = (Contact)this.getOriginalRecord();
    }

    //Properties
    public Id Id {
        get { return record.Id; }
    }
    public Id lastName {
        get { return record.LastName; }
    }
    public Id firstName {
        get { return record.FirstName; }
    }
}

SubscribeObject.cls

public virtual class SubscribeObject {
    // Make private so that these variables can't be changed all willy-nilly
    //   by anything and everything
    private SObject record;
    private SObject oldRecord;
    private SObject originalRecord;

    public SubscribeObject(SObject record, SObject oldRecord, Boolean editInPlace) {
        this.originalRecord = (Contact) record;
        this.oldRecord = (Contact) oldRecord;
        if(!editInPlace) { this.record = record.clone(true, true, true, false); }
    }
    public SubscribeObject() {}

    // Make protected accessors for your subclasses
    // Apex methods are final by default, meaning they can't be overridden
    protected SObject getRecord(){
        return this.record;
    }

    protected SObject getOldRecord(){
        return this.oldRecord;
    }

    protected SObject getOriginalRecord(){
        return this.originalRecord;
    }
}

TestCode.cls

//Code to run in developer console to test the above two classes hirerachy.

Contact record = new Contact();
record.LastName = 'Doe';
ContactObject tso = (ContactObject) new SubscribeObject(record,NULL,True); //This line is showing error.