I wonder what sort of life Nino had before you, and maybe thats why hes so scared and defensive, and uses growwwls to feel secure.
Considering the lies that person used to get you to take Nino, I would say that his life was probably not good.
He may have been a Beloved Kitten who had worn out his welcome, through no fault of his own.
Thank You for helping that Handsome Fellow!!!