He was indeed gifted. He answered the question with limited words, however, it was still correct. Elijah liked adding some information though, so he nodded his head in agreement with the legend.
"Very good, that is indeed right. Logical reasoning is needed in order to deduce that you are in a Genjutsu. As you said, this can be done, when you realize that something is off, something is physically impossible, or simply odd. This gives you enough reason to break the Genjutsu, after realizing that you are in one. However, some Genjutsu are extremely difficult to break, since they leave little to no trace that they are in actual, illusionary. The trigger, that I spoke of before, could also lead you to know that it is a Genjutsu. Since you are a Sharingan user, I will also cover the second part of realizing that you are in a Genjutsu. That would be, to notice the fluctuation in your chakra flow (as we said, a Genjustu disturbs the default balance) through the use of your Sharingan (though it depends on the level, tomoe's and what not). Chakra sensors can do the same, and once they notice, they can break it as well. Now tell me, how would you break a Genjutsu, after realizing you are in one?"