function missionAccomplished() { console.log('this text should load after a couple seconds...'); }
...but what I don't understand is why does the console.log displays the text right away, right when the game starts. Shouldn't the callback load at the end of the animation?
If your animation has only one frame then the callback will be called immediately. I may be wrong but I think you're confusing an animated sprite (a sprite with changing images) and animating a sprite by moving it around (which is what is done with the background in the tutorial).
If what you want is to finish the game when the player reach a certain point defined by the fact the a given sprite is shown on screen then you should simply check it's position, corrected by the parent group position.