Backlinks to non-existing page?

Hello everyone, today I saw really interesting thing. One guy is building backlinks to non-existing pages (~10 pages). For example his site is http://www.loseweight.com/ and I see he is building links to http://www.loseweight.com/keyword , but when I try to check that page I get: error 404 - page not found. Then I check that page backlinks in yahoo site explorer and I see more than 200 backlinks (most of them are from article directories, web 2.0 pages and so on). So, what is the secret to build backlinks to non-existing pages?

Get backlinks for a keyword, write content and then hit the no 1 spot in google instantly??
Or IDK

He's probably building out the content for them now, building backlinks before just means that the page will have "link juice" once the page is fully built out...

I do the same thing for newer sites as well if I don't have the content or "gameplan" for the website yet but have an idea of what my URL structure will be.