This is a very curious incident,
AFAIK Alt. deploy just releases the uplocks (Elect) and allows gravity to allow the gear to deploy, and I believe the Airbus uses a similar type of system.
So even with NO Hydraulics, gear should still deploy. The use of Flaps and spoilers shown in the pictures would indicate that not All Hyd. went out, nor explain why uplocks would not release ...
Kudos to the Flight crew on averting a potential disaster!!!
