I think what you need to observe is whether it has a "graft line", usually about few inches above the soil surface. If that's positive, then you know it's grafted tree, and with the seed showing, this is what you want, because you'll have s tap root growing under that seed; resulting in generally faster and stronger growing tree. (As compared to air layered tree without a tap root).
I am surprise if Home Depot is selling seedling avocado or cherimoya. But on mango, I read that they sell Manila seedlings from Lavern's nursery...