Hogwarts students didn't need to worry about their luggage after loading it onto the train, as dedicated House-elves would help put it away and then move it back to the dormitories upon arrival at the school.
Originally, Ye Feng, Harry, and the others didn't need this service because they possessed storage gear. However, since Ye Feng was simply "too dangerous," Dumbledore had specially instituted a new school rule. This rule mandated that all Hogwarts students had to place their luggage in designated areas on the train after boarding, allowing teachers to use magic to inspect for contraband.
Although Ye Feng hadn't actually caused any serious incidents yet, Dumbledore felt it was best to take precautions. Otherwise, who knew what Ye Feng—who could tinker with so many things using items obtained from the school—would come up with after bringing back a multitude of materials from outside?
Chapter 137