2 domains point to the same IP address. Likely there is a firewall or other routing device set up to point anything on the HTTPS port to the other IP. We use this here. We have 2 pieces of equipment sharing an IP address. Our SPAM firewalls web configuration interface is accessible by redirecting anything to port 443 (HTTPS) to it. All other ports are directed to our mail server.

The other way to do this is if you are running multiple web sites off a single server. Usually you would use to define the host and then Apache would have to figure out what website to serve depending on the packets rather than what port/IP they are coming from. If you did and didn't have any other virtual hosts using that port then whenever a request was made using HTTPS then Apache would serve that page up.