they used a timeline to achieve this :), to access the code go to your content browser and search for “BP_Pickup_Parent” blueprint, double click and go to “Animation to make the pickup rotate and bob up and down” section.
For more info about timelines read Timelines documentation
EDIT: to add a sphere trigger open “BP_Pickup_Parent” go to components tab and add a sphere component.
the sphere component acts like sphere trigger 