Isiah was deeply invested in his attack, he was holding lexie with one arm to prevent her from getting outside that armor as a result of her panic.
she never saw this attack as it was accuring, this was the first time isiah had anyone near him while he was doing this spell.
nelrovin was a very powerful and dangerous spell , to him it was a huge one too, because he had to stay still while people where being killed in front of him.
and even when this spell was consuming so mcuh power, isiah just didn't want to show himself on the crowd and waste his time when he could actually kill them at once without moving a finger .
during the attack, isiah felt like someone was about pulling him down, it felt like this person realized that he wasn't hurt like all of the people and he wanted drag him with them.
so he pulled hisarm outside of the armor very fast thinking that this would hurt him, isiah was too busy even to notice that.