Yatora is intelligent and scores high grades in his second year.
Even though he is insecure, he is really good at socializing with other people and seems to be an extrovert (He tags along well with Utashima, Sumida, Koigakubo and art club friends) .
I'm hoping that someone could explain me about the overlapping situation where the protagonist is both insecure and an extrovert.
I'm not sure what exactly you are wondering about, but the following line from Wikipedia article should be the answer more or less.
与えられたノルマをこなすようにして、人付き合いや勉強に励んでいる。反面、何をやっても達成感を得られず、空虚な毎日を過ごしている。
Roughly it says for Yatora socializing or getting good scores in exams are like assignments and he does not feel he has accomplished anything (because they are just assignments) and feels that he is passing the days in vain.
A natural interpretation (or I guess it is one of the stereotypes of adolescence in Japan) is that he is good at things that are supposed to give him the 'high status' (in school life), but not passionate about anything. He feels insecure because he is not 'into' anything and he's afraid that possibly he never will be (before he starts art).
As for 'hiding real intentions', I suppose you mean he does not confess the feeling of insecurity to anyone, but that is part of the socializing. He thinks telling his real feelings might well jeopardize the relationship with friends.
