I dont know if this has been mentioned before. However on impact the landing gear appears to be down and locked.
Reading between the lines.
It looks to me like they where having major flight control anomalies at the point at witch you would normally retract the landing gear. ie More or less 50ft with a positive rate of climb.
I think that they where probably flighting to control the aircraft and where ether to busy or forgot to retract the gear. I dont think this was caused bye pilot error. If is more likely in my opinion that this was ether caused bye a loading or mechanical failure/error.