The meter will have a very low value resistor between the 10 A and COM sockets. This connection will not be affected by the range switch, so you essentially connected a short circuit between the AC Live and Neutral terminals of the outlet.
When measuring voltage, the red lead MUST be in the "Volt/Ohm/mA" socket on the meter, and the black lead in the COM socket, as well as having the range switch in the correct position.