In Boruto the Movie, technology has been developed that allows shinobi to use techniques through the use of scrolls and a forearm device. Naruto disapproves of these new technologies because it removes the need for training ones chakra to do the technique without it, is a sense, it handicaps shinobi to the device. As such, Naruto banned the devices from the Chunin Exam, to make sure all shinobi were using their own techniques and chakra. Boruto was present for the declaration of the ban, but used it anyway, which is why he is declared a cheater and removed from the exam.