Well, it's not a Retusa, the leaves are different, the F. Retusa, native from Borneo, has a rounded tip on the leaves, as you can see at this KEW samples...
Ficus Retusa
Ficus Microcarpa
But you made a good point LB, I always though that Caudex-like roots is a Microcarpa characteristic, as you can see in this seedlings...
Being the top leaves also Microcarpa, maybe the grafted branches were prunned of long ago...
Well... If you look at the backside of the tree, you can see the bulb still there with a bit of a calous on top, but maybe as I said, the grafted tips were cutted off, allowing the lower part to backbud?