This highlights the necessity of:
a) making a good coding challenge [this is not, as it is currently defined]
b) defining it without any ambiguity [lots of unclear language here]
c) defining it without any inconsistency [you and I spotted the inconsistency here]
d) Talking to the candidate about the challenge in case a,b,or c are violated.
In this case, the challenge is more of a litmus test for the company using it than the candidate.