That's a good question with no good answer. I sometimes get confused with the "Inserts and Related Sets" section. Although they may be out there, I don't believe I've seen a section just called "Related Sets." Everything seems to get lumped under "Insert Sets." For example, the Inserts and Related section for the 1996 Collector's Choice has "Inserts," "Promos," and "Insert Sets." The Dan Marino A Cut Above UDA Jumbos are a related set to me, yet it's lumped in with the Insert Sets. Perhaps I'm a little too literal (or dense), but I consider inserts as cards inserted into packs.
I agree that this set could be considered a related set. I didn't want to include it as an insert set as it isn't. So, I went ahead and listed it as a standalone, oddball set.