The landing gear lever is located between the 2 primary flight displays while the fuel cutoff switches were directly below the throttle. They also look and operate in different ways. The only way I could see someone accidentally confusing the two is if the pilot flew other aircraft types where some function is located in the same place as the fuel cutoff switches.
Apparently the cockpit voice recording caught one pilot asking why they shut off the fuel and the other denying it. They were also turned back on right before the crash and were found in the on position, so it doesn't appear one was trying to force it off or anything.
It's possible it was intentional, but unless it was a terror attack from the pilot it doesn't make much sense. Since there was no manifesto or any statement I doubt that. Suicide is technically a possibility, but why take a plane full of people and some on the ground with you? I know some people lose empathy and reason when they get to that point, but it seems significantly more likely to me that the pilot was fatigued and just did the wrong thing, hanlon's razor and all that. Mistakes are more common than you would think, they're just not usually 'cut off fuel to both engines right after takeoff' bad.