I don't think MN should have to check.
But I think that thread had its own issues. I stopped reading at some point because it's incredibly long, but last I saw, it seemed to be basically:
OP: Look at this badly-worded maths question. Children find it hard to interpret.
mathematicians/people with higher maths degrees: Oh, yes, this is ambiguous, but mathematicians enjoy discussing ambiguities.
Many others (without higher maths degrees): OMG you are a terrible person OP, how dare you not know maths has a right and wrong answer, if you claim children don't understand this it must be because you are really stupid too!
I think if I'd OP'd that I would be hopping about it being promoted because it's an example of a thread where people are showing off how unpleasant they can be. I wouldn't expect HQ to have read it all in detail and I'd realize they might have promoted it just from seeing it had lots of responses and an interesting OP.
Why don't you get in touch and ask them to reconsider?