All I can find by searching is that this episode was the only one to include live action (IMDb trivia, for example: https://m.imdb.com/title/tt9788514/trivia/?r

All I can find by searching is that this episode was the only one to include live action (IMDb trivia, for example: https://m.imdb.com/title/tt9788514/trivia/?ref_=tt_trv_trv https://m.imdb.com/title/tt9788514/trivia/?ref_=tt_trv_trv) -- what makes you think it's cgi?