There are a few ways to shut off the engine without touching the fuel switches, if this happened it should have been logged, but they haven’t released the raw data.

At this point in the flight the pilot flying should have both hands on the yoke, and the other pilot is responsible for raising the gear, flaps, making radio calls etc. Definitely neither pilot should have their hands anywhere near the fuel switches, but fatigue has been demonstrated to make massive mistakes possible. Raising the gear level is vaguely similar (you have to pull it out of a detente and flip it over a notch). Of course the gear lever is nowhere near the fuel switches, but that goes back to my point about fatigue. It’s extremely rare, but the safety mechanism for the switches has failed before, if this happened it would make accidentally flipping them an easier thing to do.

But as I’ve said, intent is a very hard thing to prove. The only times pilot suicide has unambiguously been proven is when they a)locked the other pilot out, or b) were recorded ranting and raving in the cockpit. Hopefully the AAIB can determine if there was a mechanical fault. But if they determine that the switches are the reason, I would guess the final report would say the cause is “due to activation of the fuel cutoff switches for unknown reasons”, or some variation of that.

Take Air France 447, for example. The first officer pulled the nose up while in a stall and held it in that position despite every pilot learning on day one to do the exact opposite. He continued to do so even when the captain told him to push the nose down. Was that pilot suicide? A possibility, yes, but something that’s unprovable.