This statement is true.
To understand why, we need to look at the evolutionary relationships within the animal kingdom. Roundworms, or nematodes, and arthropods both belong to a group known as Ecdysozoa. This group is characterized by organisms that shed their exoskeletons as they grow. In contrast, flatworms, or platyhelminths, are part of a different group called Lophotrochozoa, which does not include roundworms or arthropods.
Therefore, since roundworms and arthropods share a more recent common ancestor compared to flatworms, it is accurate to say that roundworms are indeed more closely related to arthropods.