It happened in the Detroit of Ormuz so both side expected enemy presence there.

But honestly why would the Iranians use such an inadequate type of weapons to shoot down an apache ?

It would be like using a machinegun to kill a fly. Or using an artillery barrage to shoot a plane.

The video I used as a source mentionned the crash of an Ukrainian MIG in the conflict with Russia that got damaged by the "frag" projected by the Shaheed drone he had destroyed. So there is precedent of airplanes going down while attempting to intercept and destroy slow moving drones.

The same thing could happen to an Apache attempting a drone intercept in pitch black night.

The shaheed drone are supposed to be cheap alternatives to cruise missiles and fatigue your enemy in forcing him to use expensive equipment to intercept or accept casualties on the ground. They are not an effective anti-air weapon.