This creator claims they coded the engine themselves when they just copy pasted the same engine from a way older game on this site. They originally were working on another game with this engine, then abandoned it to start Graduation. Later, they then abandoned this project as well, right after the first updates in favor of working on the first game again while charging exorbitant amounts on their patreon and claiming updates were coming, they just needed to first "revamp the engine", probably removing anything that would jam them up for copyright while still accepting everyone's money. Their games are crappy writing mixed with porn clips so if that's your thing then go for it.