Original: Like other non-mammalian synapsids, therocephalians are described as mammal-like reptiles, although in fact, Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals.
Simplified: Like other non-mammalian therapsids, therocephalians are sometimes described as mammal-like reptiles. In fact Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals.