gorilla glass is made to protect from scratches and offers a much harder glass than the normal one it doesn't mean it is break resistant .. the angle at which the phones fall makes all the difference you will find phones dropping from shirt pockets drop 20 times and never break and you will find phones dropping from knee height even from best manufacturer like nokia break easily in its first drop ..
it depends on luck totally at which angle and surface did the phone fell , the level of vibrational impact.. had it been anyother phone in the same situation it would have broken as well, gorilla glass or not wouldn't have made any difference