Yes, when you have a term that is used as a primary keyword in more than one genre, you will end up getting some non-relevant traffic delivered within your long tail.

I would not be too concerned with the extra traffic that arrives. Keep in mind that your AdSense might also be targeted to the other meaning of a particular word as well.

What is important is that your long tail continues to show growth for content related to your actual niche. It should naturally grow over time as you get new content and more diverse keyword combinations occur on your forum.