It sounds like the story has it's flaws for sure, definitely sounds like some of the individuals on the plan defiantly new that something was going on because if they didn't their would have been a huge panick and things would have gone even worse then they did for people
Yes, I believe that there was an attempt to cover up what really happen in the hijacking of the plane. Unfortunately for those that are trying to cover up things the age of technology will not let anyone get away with anything. There is always a camera or a pair of eyes that are observing the situation.
It is difficult to trust news sources as companies are always out to protect themselves and their bottom line. The fact that passengers and first hand witnesses admit to knowing about the hijacking says everything we need to know. These passengers have nothing to gain by lying about this but the airlines and the nation as a whole has much to lose especially tourism which provides a boost to their economy.
I do not think it was an attempt to cover the truth about the hijacked plane out of Ethiopia. The co-pilot was the one that took over the plane and locked the pilot out of the cockpit. I think that many passengers did not know what was going on at the time since no demands were made at first. He was seeking asylum out of Ethiopia.
In a situation such as that, facts are hard to come by. It's hard to get objective reports from a hijacked plane, and many of the witnesses involved are traumatized. It is understandable that there would be some confusion as to the facts of what happened, when it happened, and how it happened.