There are two different issues being conflated here.
The first, as Hauke Laging notes in his answer is that, in this particular case, further clarification from the poster was not required for someone to satisfactorily answer the question. The only information still being sought was to demonstrate that the poster had made sufficient effort themselves1.
Invalidated comments are not such a big deal, they can be deleted if they end up making no sense.
The second, more substantive issue, and one that is captured by your question title is worth some consideration. Posting an answer where the question is incomplete, ie., lacking sufficient facts or details, is essentially speculative; it is a guess as to what the correct answer might be. Filling the wiki with guesses, or hedged bets designed to garner upvotes before the complete information is available is a waste of everyone's time, and should be actively discouraged.
Of the two cases, the second is clearly pernicious; the first hardly ever so. If—as a matter of policy— we were to adopt such a punitive approach to all new questioners, demanding they show their own work prior to receiving any assistance, then the tone of the community would shift, markedly, in my opinion.
My view is that it is perfectly acceptable to ask people, particularly newcomers, politely to provide some evidence of their own effort (especially if this is a homework question), but only in cases of recidivism or blatant help vampirism should answers be withheld or questions closed.
In the case of the question that you link to, my view was that it was not homework, was a decent enough question to ask here, and the subsequent edit by the questioner suggests that it was asked in good faith. Let's encourage that behaviour.
1. Note: I completely support not enabling learned helplessness...