I posed a challenge and there are a couple answers that could easily be golfed a little more. Is it fair for me, the OP to suggest edits that would help that answer? (Or is there a neutrality rule?)
That seems perfectly fine to me, and consistent with the way most users here play. If you've got suggestions to make, make them! I've even suggested improvements when I considered the answer to be a direct competitor to an answer of my own (both in the same language).
Of course it is OK. We try to be a friendly and collaborative bunch. When I see an improvement in another user's solution I point it out rather than writing my own. We I see a different approach, I write my own (time in "real" life permitting, which it hasn't much recently).
I think... if you don't know the answerer personally, give them a chance to think a little before you jump in. Because people will post, then edit, and some of their friends they send it to will offer suggestions, and then they'll edit again... it's that expansion of the people looking at and enjoying the game that makes it fun, and you won't see community expansion if you just jump in before they can do that.
If it was your challenge you have more at stake and presumably have spent more time contemplating the problem than the answerers did. You probably wrote a solution before you posed the problem (at least I did, in this case).
Reasonable rules would seem to be:
Creator of the challenge does not post their implementation until after they have accepted an answer.
The creator backing off a little and waiting for the dust to settle on a response, maybe a couple of days before commenting, might be prudent. But you should definitely be able to if you see something that could use improving.