Expired Domain Serps Question

Recently I was browsing some expired domains to purchase. I noticed a domain that when i visit it from Google, it shows the godaddy expiring page. But if i visit the same domain and put the http://www. Into it then it goes to the original functional site. So if i go directly to the site like this website.com it goes to expiring godaddy action page. If i go to www. website.com it goes to the last website that it was hosting on. I am just noticing this, maybe its something common. But can anyone explain this?