Let's put this in the context: the article is about problems which are supposedly killer problems because they require some hard-to-get hint to solve. Therefore, a hint is low quality, if another hint exists that is simpler, more elementary, or the problem is solved straightforward anyway.

In this case, a simpler hint is: "Do not use derivatives or anything fancy really. Only solutions are constant functions. Proof by contradiction. Use binary search".

One may only wonder what level were the problems given to regular candidates.