It’s probably not the CSS, but my guess is it’s something related to this specific setup. Maybe the language in use or the RTL CSS or integration with WordPress. bbPress does this by default when you type something that looks like a URL. Here I will just type something and bbPress will just linkify it: http://www.google.com (I typed www google com but with the periods in it)
What sort of SEO stuff do you want to change on your forum? Many people have added various seo-related tweaks without a big plugin. Post what you’re looking for, in a new topic and people will reply there. Thanks.