Hi,
Yes, you are right. You can assign a form to a category and as well as for a single product.
1. To assign it for a category of products, the option is there in the right side of the form builder. It is as same the the pages, products, etc are being assigned.
2. To assign the form to a specific product, go to the product edit page at the back-end and scroll down to Product Data section. Change the tab to Custom Product Options and Select the desired form from the list of forms shown there.
If you have already assigned another form as category-wise for the same product and you want to override that form to assign a new form for this specific product, please do tick the option “Exclude/ Override the Globally assigned forms”.
Thank you.