Where is the "%" showing up? I only see it before he runs ggc. It is common to use "%" instead of "$" in some shells.

In particular, C Shell (csh) and Tcsh uses "%" as the prompt character. Common in BSD systems.

Of course you can customize Zsh (or Bash) to show "%", too.

Edit: never mind, I noticed it when he quit "ggc". My bad. :)