Well, yes, that's true, but for exemple in this case he said "I'm working hard on your christmas renders!", so if he's only switching the characters on premade scene, that feel like a scam to "make-believe" he's working ^^
Otherwise, there's no problem in using assets, as long as you don't make it seem like your own hard work ^^
(By the way, in this game, I still didn't see any "script, code, game optimization". Well, I'm slighty wrong since for the first time, we got a "remembered" choice with the fact that you use or don't use the drug on Keiko ^^ But that's all, there's no work to do in ren'py in this game beside showing the right image with the right text ^^)