Other than the three types you mentioned, I come across another type. They don't learn new stuffs that quickly. They might look dumb when they are introduced to new things. However, given more time, they are able to think and dig really deep.

Then it occurred to me that they were already thinking wider and deeper from the beginning. Because the knowledges conveyed in an introductory scenario is so limited, they have more questions and they get confused. They have no intention to hide their confusion. Once they acquire more knowledges in the field and organize the pieces into a system, they start showing how deep their thoughts have gone to.