Website SEO gone wrong.. OR.. Did it?

So I want to share my SEO story here. Its a kinda weird and its the first time I have seen something like this. Basically I have been working on this website for a while and have been doing huge amount of SEO for it. The website is 3 months old (its a blog), and all my SEO work is white hat with some grey hat here and there.

After 3 moths of building quality back links, etc, I have been fluctuating between page 2 and 3 in Google. The keyword I am trying to rank for gets about 5000 monthly searches on Google. I have been on yahoo page 1 for a while. Anyways, I was getting about 200-300 daily uniques from search engines.

So recently I checked my website and saw a huge spike in my traffic, Google was sending me over 6000 uniques daily! After further investigation I found out that I am on page 1 of Google for a completely different keyword. The keyword get over 800,000 searches on Google a month! and is extremely competitive. I mean if I told you the keyword, you will be like WOW. The worst (or best) part is I didn't target that keyword at all! Never used it in a single anchor text for backlinks, don't have the site optimized for it.

I checked and saw that I am still on page 2 for the keyword I actually wanted to target, and the keyword is not even close to being as competitive.

But there is a problem, my site doesn't really relate to the keyword I am ranking so high for. Basically all this extra traffic is going to waste.

What do you guys think about this? Have you heard of something like this before? Do you think it is only temporary? Should I make changes to my site for the new keyword?

Anyways I just thought I would share with you guys.

EDIT: I do want to add that indirectly the keyword is mentioned in the content of the site, but never was it really the focus.

I never came across something like this, probably a google dance, but you can still squeeze the shitload of money maybe.

if you know how to use php:
- in header, very first rows, write conditional loop that checks for refferer (googe.com/?q=keyword), be smart about it, use regex as the refferer might look a lil bit different for various browsers, the only thing you are interested in is the "q=keyword" part !!
- find some good CPA, affiliate or whatever for making money
- redirect all traffic from this keyword

might just get you some nice amount of $

Just leave the page as is, except provide a newsletter opt-in with a promise to give valuable information for the big niche, and then mail them some appropriate offers.

i would redirect them all, maybe try few sponsors, redirect equally to them, eg. 1 : 1 : 1 and find out about which one is the best

opt-in isn't the best choice imho, many people simply don't like giving away their email address, those that do are probably more vulnerable to become buyers, but you're losing the rest