What if someone posts an answer which, in fact, doesn't answer the question? What if, in addition, it is claimed in the answer that the question "is wrong"? Are there any moderating rules regarding such answers?
Generally wrong answers should be down-voted. You can comment on the question and hope that the poster edits or deletes the answer. This could lead to a comment-debate, which will eventually be drawn to the moderators' attention, and we can decide whether to do something about it. If the answer adds nothing to the discussion, a moderator may delete it.
Another option is to flag the answer for moderator attention, but this won't necessarily mean that it will be deleted. If it truly doesn't answer the question, this might result in a moderator down-voting the answer.
In any case, if it does not answer the question, you can (implicitly) indicate this by not accepting the answer.
Jeff's answer may not be the answer you are looking for but it doesn't mean that it is not an answer, I personally think it is a good answer to the question.
You are free to choose to accept whichever answer you like most, and you can vote on answers as you please. Other users are also free to post answers and vote as they please. Looking at the votes, it seems that other users think that Jeff's answer is a good one. You cannot restrict the answers to those answers you like.
If you don't like the answers you have got so far then check this FAQ entry: What if I don’t get a good answer?
If you ask a question and see no answers you like, one course of action is to put a bounty on the question. You can even specify in the comments the type of answer you think would get awarded the bounty. This would incentivize people to answer the questions your way, as you'd be the one to determine who gets the bounty.
One note: you need at least 75 reputation to offer a bounty.