In 1.92/2.10 quests, the Rope 2 should use CSet 9. However, it instead uses CSet 8. CSet 8 should only be used for quests using that rule in 2.50 and above, which was probably a change made to make the Aineru (the new graphic for Rope 2 in 2.50's classic tileset) look more Z2-like.
This can be seen in several 1.92/2.10 tilesets like NewBS and Dance of Remembrance which helpfully label what CSet enemies use (unchangeable in those versions).