* Wombats belong to the order Diprotodontia, which includes other marsupials like kangaroos, koalas, and possums.
* Numbats belong to the order Peramelemorphia, which includes bandicoots and bilbies.
This means that wombats and numbats share a common ancestor much further back in evolutionary history than "cousin" relationships usually imply.
Think of it this way: They are distant relatives, like members of the same extended family, but not close enough to be considered cousins.