We're glad you liked our game!
I'd love to explain how I did stuff, just ask away and you shall receive <3
For the piece pickup I do a raycasting from bottom of the grabber and when it hits a piece it is identified by it's variable ID.
The raycasting activates when it enters or exits the first piece (or group of pieces).
So to be able to pick up a correct piece from a pile you'd have to position the grabber inside the piece to be picked up.
Try to play some harder difficulties as well as you can change the difficulty in options menu.