Richard Wunsch called the group Sethian, and the name has been attached to it for well over a century, but it carries a claim that most scholars no longer accept. The tablets invoke a figure whom Greek and Roman writers of the period identified with the Egyptian god Seth, equated in turn with the Greek Typhon: a power of storm, violence and disorder, which is a coherent choice for a text meant to wreck a race. That much is in the tablets.
Wunsch went on to connect the group to the Sethians, a Gnostic movement known from the heresiological literature and later from the Nag Hammadi texts. That step required the two uses of the name to be the same thing, and there is little in the tablets to support it. The Gnostic Sethians are named for Seth the son of Adam, not for the Egyptian god, and their surviving literature has nothing to do with chariot racing.
The atlas records the attribution as debated rather than simply wrong, because the label persists in the scholarly literature as the standard designation for the corpus and because arguing that a name is only a convention is not the same as demonstrating that no connection existed. What can be said with confidence is that the name describes the god invoked, not the religious affiliation of whoever paid for the tablets, and that a reader meeting the term Sethian in this context should not take it as evidence of Gnosticism.