I'm curious as to how you ended up with /forum/forums though? I'm guessing you uploaded the "forums" directory into your already existing "forum" one? I'm pretty picky with how everything looks and while adding a route filter to remove /forums might be the best and easiest way, if you only just installed the forum and have nothing on it, you can consider deleting the entire directory "/forums" and simply uploading the forum files (not "forums" folder) into your existing forum directory instead.
This basically means you'd be re-installing the forum again but it would permanently be in the first /forum directory if you did. It's really up to you how you go about it, I'm just picky like that.
If you do this: Remember to re-create the Database too.
If a site is a community site first and foremost, it seems like the most logical solution is to just skip the whole "community" folder and instead just install Xenforo in the site root directory. Otherwise, if you do decide to create a subfolder and call it virtually any term other than community, the URL's can easily start looking strange like the OP mentioned.