It looks like there is only one alarm flag per device. To determine if the alarm is a HIGH alarm or a LOW alarm you have to read the current temperature and compare it to the two alarm temperatures. Something like this:
if (sensors.hasAlarm(deviceAddress)) {
float tempC = sensors.getTempC(deviceAddress);
if (tempC != DEVICE_DISCONNECTED) {
if (tempC >= sensors.getHighAlarmTemp(deviceAddress)) {
// HIGH alarm
}
if (tempC <= sensors.getLowAlarmTemp(deviceAddress)) {
// LOW alarm
}
}
}