I think it must be more than a hydraulic failure...the DC9/MD80 emergency gear extension system is almost bullet proof if it is properly maintained and inspected prior to takeoff. I noticed that the flaps were extended for the landing ( hydraulic only)
a handle beneath the copilots left leg allows for a free fall of all gear ( slow down and do a checklist first of course).
this handle pulls a cable releasing uplocks on main gear doors and nose gear...there are two giant springs on the nose gear to help with extension...the md80/dc9 could lose every drop of hydraulic fluid and still land in very good order...full manual reversion on rudder, elevator, and aileron...
I have seen missing springs in the nose gear well but one must look closely during the walkaround...I've heard one break in flight...spoinggggggg.
I can only imagine that some other defect, perhaps like the american MD80 in which the up lock release was compromised (can't remember exactly what it was) may have happened again.