Let me describe one question that was closed for being "too broad" that might support the idea that closure is a trapdoor function.
The question is Why did the United States want to “make Europe prosperous once more” with the Marshall Plan?
As originally posted, the question certainly did appear to reflect a certain bias, and this was noted in the comments. However, based on the OP's later comments in response to my answer, I realised that it was actually probably just a question of language, rather than bias. It is all-too-easy for someone whose first language isn't English to equate the terms "self-interest" and "selfishness". I edited the question accordingly.
I have been meaning to add a link to the appropriate volume of the Congressional Record, so that the OP (and any others who are interested) to read the official record of the debates on the Act in Congress (especially since, in the context of self-interest, it is illustrative to note how often senators mention specific benefits to their home states when discussing the Marshall Plan).
Because of other distractions (and the fact that the search tools on archive.org aren't really geared to multi-volume publications like the Congressional Record), it took me a while to find a publicly accessible link to the right volume. When I did eventually get around to it, the question had a re-open vote, so I thought that I would wait and see what happened.
Now, as the question currently stands, I would say that it is clearly "a specific problem with enough detail to identify an adequate answer" (as required in the help centre). Despite this, two-thirds of those who voted said that it should remain closed.
Now, it may be that they feel that the question should remain closed for other reasons. Those reasons may be entirely valid, but they are not recorded. In a case like this, how can an OP be expected to improve their question if they don't know why it was closed?
So yes, based on this, and my experience of trying to get a question that was incorrectly closed as a duplicate reopened, I'd say that closure does indeed seem to be a trapdoor function.