Yes it did. That's the point of the example.
The game rules stipulate that, at the end of the NPC's next turn, the Baleful Polymorph ends. The rules do not stipulate why this occurs. (Thus, the mechanic is similar to the War Devil's mechanic that The Alexandrian lambasts in his essay.)
In the fiction, why did the curse on the paladin end? The answer - because the Raven Queen turned him back. And that answer was authored by the player.
EDITED TO ADD:
There is a more general issue for playing religious characters, if you interpret those sorts of player remarks as reflecting nothing more than the conjecture of the PC.
The actual resolution mechanics of D&D generally involve either deterministic rules - "This effect ends after 1 turn" - or dice-rolling rules - "This effect ends if the player rolls a successful save for his/her PC".
If the player is not allowed to narrate in the fiction the role of the divinity in brining about the mechanical effect, then the PC's religious conviction is in fact shown, by the mechanics, to be irrational - because no good outcome is ever, in fact, a result of divine providence but rather is the result of the impersonal mechanics (whether deterministic or random) of the cosmos.
This is suitable for playing a Conan-esque game, in which a belief in providence is either delusional or charlatanry, but is not at all suitable for a romantic or Tolkien-esque game.
I have two responses:
A) This would make them no different from faithful people IRL. (after all, they can't
all be right.) That is, in a D&D style gameworld, things happen...weird things that aren't mundane like people turning into frogs. However (in games like D&D) these supernatural events and powers have durations, etc. that end up functioning like a kind of physics (even if a poor one).* Your character's assertion isn't even comparable to a Priestess of the Goddess of Momentum praising her for the bowling ball making it to the end of the lane. Why did the Baleful Polymorph end?-because effects like Baleful Polymorph do that.**
B)...except that there
are (or can be) mechanics (bonuses, etc.) that
do (or can) reflect a deity's intervention. So if we know that the Priests of the Goddess of Momentum are immune to immobilizing effects...then a PC can legitimately give her credit for that. The same for spellcasting abilities, etc.
*There are other games and mechanics, even some within D&D, for which this is not the case or at least not necessarily so, as the character's experiences would not correspond 1-to-1 with the operation of the mechanics.
**And I apologize for skirting the community guidelines.
EDIT:
Also, are characters in your game never
wrong when they make assertions outloud? I mean, this reminds me of folks in various fandoms taking quotes from characters as gospel truth....forgetting that characters can be mistaken. So one character asserts "the Raven Queen did it" and is automatically presumed to be speaking the truth, what if another character asserts "I am invulnerable!" is he not automatically afforded the same consideration or do faithful characters receive some special benefit for declaring things in fiction?
ADDITIONAL EDIT:
D&D is, I think, solidly in the Conan camp. Its earlier incarnations are all about tomb-robbing murderhobos and nihilistic meaningless death due to a failed save, etc. Making D&D more romantic or Tolkienesque, I believe, requires heavy-handed DM intervention in the mechanical operation of the game....thus all the railroading in the old days. However, it occurs to me that this shouldn't bother players looking for that experience, because, after all, they are looking for a world where some personal divinity
is actually looking out for them. In this case its just the DM.