jamesbond6,
You wrote:
"The latest news (released by press/airport authorities, not the airline, so please consider some bias on accuracy) on the technical part of this topic is that the gear has been extended from the inside of the aircraft (I assume it means cockpit) by the engineers sent by Boeing. So could it have been possible after all?..."
Another explanation could be that the fault in the alternate extension system had been found and rectified!
I doubt that the crew made mistakes - they had lots of time and apparently had great help from the company - see #189 below
#189:
they were in touch with ops, mechanics, and training captain, and circuit breakers were one of the first things they checked, and quite extensively. We we listening to their freq on twr.