Hi Mocquin,
As the words “ray” and “split” are the same in both expressions, I assume the “NSC” is what you find confusing: It means “Non-Sequential Component”. I guess it was too long to write fully (this dialog dates back from the early 2000s, when screens were much smaller). Perhaps “Non-Sequential” would be better.
If you refer to the “Split” vs “Splitting”, it looks consistent with usual standards:
“Ray splitting” in the documentation is a topic, for which a name form is a common way (see the other sections of the documentation, most are in nominal form, “Editors Group”, “The Setup Tab”).
“Split Rays” is using a verbal form because that is the standard in graphical user interfaces (“Save Rays”, “Use Polarization”, “Trace”, “Clear”, “Exit” but also in the older “File”, “Edit”, “Format” menus)