That Pumptrol switch has a low pressure dropout feature built in to it. The idea is if the water level in the well is too low, or if a line suddenly ruptures, the pressure will drop and the pump will shut off. On a 30/50 switch, that dropout pressure is usually around 20 psi.
You don't have to have a complete dry well condition for this to happen. As the water level in the well drops lower, the pump will begin pumping less water. If the demand is greater than what the pump can supply, the pressure will drop and the pump will shut down. You haven't completely ran out of water in this scenario, but the switch "assumed" you did, and reacted accordingly. As you found out, holding the lever up will restart the pump.
Try monitoring the water usage, keeping an eye on the pressure gauge. If the pressure drops and the pump can't keep up, shut it down for awhile and let the well regenerate.