Well, I guess it depends on the direction of the current flow you're trying to interrupt. It seems to me that when you are charging, the flow of conventional current is from the positive charging source into the positive 2S terminal, out through the negative terminal to ground (which is the negative return point of the charging source). Ground is the lowest voltage point in the circuit. In that case the drain should be at 2S- and the source at ground, and the body diode would block that flow when the mosfet is off. But that is not what's shown in the drawing.
When discharging, the flow is from the 2S+ battery terminal out through the circuit to ground and then back into the negative 2S terminal. 2S- becomes the lowest voltage point in the circuit. In that case the drain should be at ground and the source at 2S-, and the body diode would block that flow when the mosfet is off.
The DW01 datasheet shows the double-mosfet circuit Daixiwen described, but the DW01 only works for 1S.
I guess I still think the mosfet is oriented backwards in the drawing.