hydraulic seals break all the time. especially when you dont take care of the jack and maintain it. what was the extra 30 second to put a stand under the car? Use an old rim or firewood! I feel scared when i dont have the stands under there.
Almost happened to my friend, He had his s2k jacked up as high as it could go on the diff and a friend was suppose to put jacks under but he didnt hear, happened when he was doing his exhaust and to get it aligned he had to literally throw all his weight side to side to move exhaust the whole car was shaking and surprisingly jack held up but every time I jack up my car I think about that moment and put jacks under and check twice.