Maybe they specified the challenge in this half-assed way to deliberately test those sorts of skills (even if irrelevant to the job), or maybe it was just lazily put together.

The other thing to note is that if you look at what the reference_kernel() is actually doing, it really looks like a somewhat arbitrary synthetic task (hashes, wraparound), so any accurate task specification would really need to be a "line by line" description of the steps, at which point you may as well just say "here's some code - do this".