It's a trick a lot of subversive indie games use. Basically the game searches for the user file that usually named after you, and then it repeats it in the game. It's spooky at first but it gets dry when you see it done too many times.
Subversive? Very funny. It's a simple environment variable call on Windows. As with all EVs, this is information available to any and all apps without any complex code. On late versions of Windows, it's simply %USERNAME%; on earlier ones, you would strip it from the end of %USERPROFILE%. No searching is needed at all.
Right-click the start menu, choose Command Prompt and enter the following:
ECHO %USERNAME%
And see the "magic" of subversion. Want to see some more? Simply enter:
set
The reason big name games don't do this is because it's very unlikely to be your username although it might be the first five characters.