On a very mundane level, it merely means that this quilt was inherited from somebody.
"Heirloom quality" - i suppose is one that is "better" than most other quilts.
I would say that anything that feline fanatic quilted would be in the "heirloom" quality.
There are also some other longarmers on this board that do extraordinary quilting.
Are there separate categories for hand and machine piecing, and hand and machine quilting?