It would be better to have a Pre-Sales forum staffed with people who have experience in sales. If you made a potential customer feel uncomfortable or unwelcome (and a combative attitude, coupled with information that is plain wrong, will do that) then yes, it's unprofessional.
Here's the kind of response that would probably be more conducive to a sale:
"Hi there! We understand that SEO is a huge priority for site owners and that SEO needs vary from customer to customer. While XenForo doesn't display forum names in the thread title out of the box, it is an extremely easy modification, and our community members will be happy to guide you through it. That said, XenForo is designed with SEO in mind and routinely outperforms other forum packages in parameters X, Y, and Z. I think if you try it, you'll be pleasantly surprised with the results."