As in we the readers took the word “seal” to mean like Naruto type “seals”… that’s not what it is… It’s like me saying I “sealed” my watermelon slices in a plastic bag…
Get it? It’s not that Emeth had Joyboy’s haki to use like his own haki… and it’s not like Joyboy put haki into material of an object… Joyboy set off a haki bomb and just put it in a random container… And then the container was opened and the haki bomb went off
Get it? The rope that the haki bomb was in wasnt suddenly empowered to be some kind of “black blade rope”… it’s just a container for a haki bomb… emeth couldn’t put out the Rope and start using bits and pieces of joyboy’s haki… The rope is just to stop the haki bomb from exploding… It doesn’t have haki inside itself