Your FACE is glitchier than skyrim! j/k.
Also, yeah, in a large sample (LOTS of attacks overall...) it would be improbable to never miss 4 times in a row. Chances are about 1/3000 for a given string of four attacks.
I have a challenge for you -- redo 19 without using recursion. My solution took 24 boxes and 4144 steps. That's with a pretty tight solution for 8, and I bet there are places it can be improved.
It would be fun to see total boxes/steps as some kind of high score (or low score!)...I'm curious to know where I could optimize better. With more boxes/less steps on isEmpty, I can get lvl17(7/799) and lvl18(7/810), but I have no idea how you can finish lvl16 with 7 boxes.