With the shield active, Alex didn't fear charging into the hoard of goblins before him. First, he was stronger than them and second, having attained rank 3 Warrior, his strength was high enough for him to deal with these pipsqueaks that took themselves as elites. Well, they may be elites of goblins but in Alex's eyes, they were nothing but trash.
It wouldn't be good to call them so as had Alex met them that morning before he entered the tower, he wouldn't have lasted a few seconds, let alone defeat these 'trash'. As for where his confidence came from, he was stronger compared to normal rank 3 warriors and to add to this, he had eighty attribute points that he could freely distribute to an area where he would be lacking during the fight. So, why should he be afraid?