In the "Children of the Magenta Line" video they tell you to hold the throttles physically in place in similar situations, but not this one exactly. They want you to hold all the controls when turning on or off autopilot, changing modes, or if you think something is going wrong (this kind of plane has multiple autopilots, so weird stuff can and has happened). I guess what you could do in this case is touch the throttles to make sure they are doing what you want, and retain the ability to grab them and push them forward if the auto-throttle system is not doing it.