You had just arrived at WCKD. They had found you surviving out on your own in the scorch, and forcefully took you in.

There was a lot of kids in the cafeteria, (including Newt,Thomas,Minho,Frypan, and Aris) and you had seen everything from the scorch.

Janson led you to the cafeteria, to introduce you to the other kids in the cafeteria.