Comment Obviously the copilot saw the switches thrown (Score 1) 90
What's missing from a lot of this discussion around "What happened?", trying to find alternate explanations, is that it's clear the first officer immediately knew what had been done.
If the engines had unexpectedly shut off a few hundred feet off the ground during takeoff, the reaction wouldn't be "Why did you do that?" with a very quick reversal of the action, it would have been a callout of the situation and troubleshooting.