So you're saying, that in reality external to the mind, there is such a thing as a thumb?
It depends. Is there such a thing as sound?
In the external reality, there are quarks. My body is a particular set of (continually replaceable) quarks that more-or-less obeys my mind; besides, my mind has privileged access to the sensory inputs of this body, so it's justified to consider it as distinct from the rest of reality. A category like "thumb" is a shortcut entry that is very useful to refer to a subset of quarks that stay in a very specific, more-or-less constant configuration.
So, does my thumb exist? Yes, in the sense that a bird flock exists because some of them fly together.
I did a search about property dualism and I couldn't see much written here on this site.