I guess the question is how bound the DM is by those rules, they could have let the chars find another item, it is one they chose. I am not sure how the rules of the RPG played into what was chosen, but the arrows had some meaning to the chars already. On the other hand, there are probably several other items that do too and could have been chosen instead, giving a different spin on the event.
Well, arrows or whatever aside, narrativist systems, at least of a PbtA sort of ilk (and I'd say FitD, and Agon both also exhibit this, and BW has a pretty strong flavor of it too) the GM being cast in a specific role which includes following certain rules is a VERY important aspect of the process of play of those games and how they are structured. I mean, sure, the GM and the players are only as much bound by the rules of an RPG as they feel like, but if you ignore these concepts in play you will be playing a very significantly different game in fundamental ways! A GM in Dungeon World can ONLY make moves as described by the game's rules. The moves they make, and way they frame scenes, and the prep (fronts and maps) the develop are specifically intended to fulfill goals which support the agenda of the game. This agenda includes, centrally, a game which shares direction between the different participants, by design.
So in either case the DM directs what is going on. That is why I initially said I am only seeing degrees here, not fundamental differences.
Dungeon World and D&D, as examples of generally Narrativist and Trad games, are fundamentally different, trust me. The GM does not 'direct what is going on' in a correctly run Dungeon World game. Yes, they frame the scenes and introduce elements via moves, so they have a part in direction, but they can only introduce stuff that plays to the characters. The GM's part in decision making DOES NOT function to put bounds on play.
The main difference I am starting to take away from all of this is that BW and similar games are a lot more formal and rules-oppressive (do not want to say heavy, that term is already taken), pressing both the players and DMs in a formal rules corset of interactions, much less freeform than D&D.
I am not saying that makes the game more restrictive, the players probably can do essentially the same things they can do in D&D, but how they go about it is much more dictated by the rules. Or at least it looks like that to me
They are no more 'rules oppressive' than D&D. What can be more 'oppressive' than a GM with absolute power and only the most informal of mechanisms (basically complaining) by which anyone else can get a say outside of "my character says X"? D&D is far LESS freeform than Dungeon World, for sure! The rules of DW simply clearly establishes how the process overall is supposed to work. Its actually IMHO empowering and freeing as it clarifies play immensely and lets it be centered on what is interesting in ways that are difficult to achieve in trad play.