You just received your starter from the teacher. the starters were from regions and were random. you were supposed to get a Mudkip, but, in reality, the mudkip turned out to be a ditto that mustve was mistaken as a mudkip, because of its ability to transform. The professor was going to get you a different starter, and take ditto away, but you convinced him to let you keep it. the other students got cool starter pokemon

The scared ditto looked at you, still sitting on your desk, before looking away, scared