The arm you're seeing on the hub is to engage the (probably drum) brakes, and the rear probably is also an IGH instead of derailer/sprockets. (IGHs and drum brakes are a lot more environment-tolerant and harder to screw them up accidentally (or even vandaliciously) vs disc or rim brakes, so makes sense to use them).
The "finger" on the fork that engages the "U" on the hub might be to engage a cover-sized torque arm, if this is a front hubmotor. Otherwise it is to give the brake something to react to (just like a hubmotor, the drum brake (and IGH) have two parts that push against each other to work, so the nonrotating part has to be very secure to function without damaging the frame).