To turn that off go into CP->Primary Settings->General->Advanced Options->Uncheck show debug info.
I wouldn't get too caught up on key search term like that. Often on a message board there will be a search term not related to the boards content that will be popular in searches. For instance on my board if you search "really big housecats" we come up in the top 4 for that. Terms can get much more "graphic" as well.
If you are interested in SEO read a lot of Matt Cutts stuff, follow him on twitter. SEOMoz has a great blog, and there is tons to read on Webmasters World. There are obviously a lot of good and bad techniques available, and you could hire a team of SEOologists to "optimize" your site, but as I've said before in another thread the best thing you can do for SEO is just run a really good community and things will take care of themselves. Content is king!
