This is not possible using the standard comment form. Comments in WordPress are built around post IDs, and are coded with this assumption down to the foundations. Even post statuses that can receive comments are hardcoded at multiple levels.
The comment form itself knows where to go afterwards via the comment_post_ID input.
You will not be able to repurpose the existing comment form to submit comments and have them handled via the normal method. You will need to rebuild the comment form from scratch, as well as the code that submits the comment, and the server-side comment submission handling.
Additionally, comments are intended for posts, and your comments on these custom table records will show up on random posts and attachments, as well as mangling comment counts and sorting