When Namecheap used to be a reseller for enom we had opt-ins all the time since enom is a premium member. It could be that your domain has a tag somewhere from enom or from another 'premium' registrar and afternic's system gets confused.
I transferred some domains to Namecheap to test if they were elegible for Afternic fast transfer and they weren’t. They also can’t be added to Sedo MLS.