Why on earth would a "talented hacker" do anything other than the easiest effective method? If it doesn't work, then just try something else. They certainly wouldn't waste their time trying to hide code snippets in a GIF when you could just upload the above.
In short: the "talented hacker" is the one who compromises your system. The difficulty of execution does not matter if you get owned in the end.
The astute reader will also note that Five and Six were also not discussed. From the fourth paragraph, "I will be discussing a subset of the nine challenges".
The attack could also have been a lot more interesting if .php files were disallowed but short snippets like this could be hidden inside GIF images.