Marvin Mumbee was a kid who loved all things fiction. Science-Fiction, Fantasy, Adventure Story, Gothic, Historical Fiction, all of it, whether it was books, TV, or movies. His father introduced him to his favorite of it all: Star Wars. He was obsessed with it from the very beginning, so much so that he began to speak like his favorite character: Yoda.
Sure, it was odd at first, it's not like he spoke like him all the time, but it turned into a sort of coping mechanism he used when he didn't feel safe or when he was uncomfortable.
The time he spent at the school was a nice one, I suppose, making friends with the kids and teachers in his class, taking trips to new places to explore. One of those places was Chernarus. Whether it was to explore nature or to take the kids to somewhere new and foreign, we don't know, but he was stuck there with his friends, fear creeping into his mind every second of every minute of every hour.