They learned because they were ready to learn that particular information. Listening to a teacher talking about magnets would not have worked as well. A television program on magnets wouldn't have been effective either. Neither would worksheets on math concepts. Teachers have found that young children learn best this way.
Children move through stages.
They are ready to learn at different times and at different paces. Children learn best when teachers provide activities that are at just the right stage for the child. She can cut the playdough easily. It doesn't turn sideways if she holds the scissors wrong. She would be very frustrated trying to cut the paper.