I think he only consumed force sensitives. It's worth noting that the Miraluka are a force sensitive species.
It's not that he was only capable of consuming force sensitives. Those just fed his hunger (temporarily) much more than other beings. But all
life on Katarr was fed on by Nihilus---except for Visas, the only survivor, who said "every living thing on Katarr died", which seems to imply not just force-sensitive sentients. All life is touched by the Force, after all. Jedi are just exceptionally sensitive to it.
By the time of KOTOR 2 his hunger was probably so strong that only other force sensitives could feed it noticeably, but if he'd gotten more desperate he could have fed on non-Force sensitives.