The first guess for each doodle was the word that was provided -- if this software was completely legitimate, I would think it should have guessed the same word for each (and then moved on to other guesses).
A good test for that would be to script the game and give it pixel-identical answers for each questions and see if the result is different.
I guess a star is a zig zag looping on itself, kinda.
For instance, our sub-conscious tendency when drawing stairs would be to have straight lines at 0 and 90 degrees but a "zig-zag" wouldn't necessarily have that feature. Thus, even though you thought the drawings were the same, there were sufficient detectable differences for the AI to recognize.