(warning - speculation ahead)
If it was hijackers, maybe they had rudimentary instruction about 777 systems from online sources or MS flight simulator, had a (poorly thought out) plan to take it over & fly it somewhere but after they got control of the plane, got the transponder turned off & turned west discovered they discovered they were in over their heads, made a bunch of mistakes & and ran out of fuel over the Indian ocean & crashed.
but using a cheap flight sim with a good database would be good practice for learning switchology (turning off transponder, data, etc) - and doing basic 2D navigation - but probably lousy for actual control of a big airplane, fuel management, and all the other stuff that goes on in flying an airliner
I'm sure there are other plausible scenarios. This will be really ugly when it's sorted out.
I think its more complex than that
Keep an eye on L1 in flight......that's all I will say.