I’m not suggesting that CSE/IOE necessarily have the best/worst engineering students, but that in general, there is a significant difference in the student bodies as a whole. To clarify, when I say significant, I don’t mean it in the colloquial sense, but rather that the difference isn’t just due to random chance.
As for your reasoning, you can’t just compare CSE/IOE GPAs at face value. You’re making inherent assumptions that the courses are similar in difficulty and that the student bodies have the same academic abilities.
As others may have stated previously, there is obviously no way to prove my claim since there is lack of meaningful data. One argument that I would pose, is that you often hear about people starting out in CSE and eventually dropping out due to course difficulty. I’ve never heard similar cases in IOE. Can you honestly argue that any undergrad IOE courses are truly difficult? In particular, I doubt you believe that any required (core) IOE course is comparable in difficulty to something like EECS 281, which every CS student takes.