However, transfer students take lower level courses at one school and upper level courses at the other school. So it is not surprising that the students found the courses at the second school to be more rigorous than at the first school, because they took upper level courses at the second school versus lower level courses at the first school.
Some might suggest graduate students as other examples who experience more than one school. But a student taking an undergraduate course seeing the material for the first time may find it more difficult than when s/he is a PhD student TAing that course at another school after having lived and breathed that general subject for years.