the game definitely wasn't suppose to end at wave 4, my guess is that the dice the girl rolled fell off of the play area and started to fall onto the safety nets below which should have caused the game to still continue, but the dice were probably thrown too far away that it even missed the safety nets and instead softlocked the game. (also the reason why the only kind of enemy was so bland, it took too long to try and save the scuffed dice throw)