8 spaces?

Probably because this is similar to the Linux kernel programming style. Many of us learnt C from the kernel or projects that follow it's coding style.

Assuming you mean the code on github, I use tabs for indentation in vim, but have tabstop and setwidth set to 2. So if the code has 8 spaces, that is github or the browser. Feel free to make a pull request, or I can try to fix it (though I am kinda focused on my portfolio for internship applications atm). Should be a simple regex though.

  perl -pi -e 's/^(\t+)/"  " x length($1)/e' recurse.c

seems to do the trick; vary the number of spaces inside the "" to taste.